REPORTS 

ON   THE 

TOTAL  SOLAR  KOLIPSE 


F   AUGUST  1,   1869. 


S;  NAVAL  OBSEBVATORY 


G01MODOREB.F.  SANDS  U.S;N. 


SBPERIHTENDBINT. 


rmitg  of 


No. 

Division . 

Range 
Shelf. 

Received 7?M4^?ff...  .   1 87; 


REPORTS 


ON 


OBSERVATIONS  OF  THE  TOTAL  ECLIPSE  OF  THE  SUN, 


U GUST    7,    1869 


CONDUCTED  UNDER  THE  DIRECTION  OF 

COMMODORE   B.  F.  SANDS,  U.  S.  N 

SUPERINTENDENT  OF  THE   U.    S.   NAVAL  OBSERVATORY,   WASHINGTON,   1).   C. 


WASHINGTON. 

GOVERNMENT   FEINTING   OFFICE. 
1870. 


IN  THE  SENATE  OP  THE  UNITED  STATES, 

February  8,  187U. 

Kesolceil,  (the  Souse  concurring  therein,)  That  there  be  printed  one  thousand  extra  copies  of  the  report  made  by  the 
officers  of  the  United  States  Naval  Observatory  of  the  total  eclipse  of  the  sun  of  August  seven,  eighteen  hundred  and 
sixty-nine,  for  the  use  of  the  Senate,  two  thousand  extra  copies  for  the  use  of  the  House  of  Representatives,  and  five 
hundred  copies  for  distribution  among  scientific  bodies  and  individuals  by  the  Superintendent  of  the  United  States 
Naval  Observatory. 

Attest:  GEO.  C.  GORHAM.  Secretary. 


Ix  THE  HOUSE  OF  REPRESENTATIVES  OF  THE  UNITED  STATES. 

J/uj/  12,  1870. 

Retained,  That  the  House  concur  in  the  foregoing  resolution  of  the  Senate  to  print  one  thousand  extra  copies  of  tin; 
report  of  the  officers  of  the  United  States  Naval  Observatory  upon  the  total  eclipse  of  the  sun  on  the  seventh  of  August, 
eighteen  hundred  and  sixty-nine,  for  the  use  of  the  Senate,  two  thousand  copies  for  the  use  of  the  House  of  Representa- 
tives, and  five  hundred  copies  for  distribution  by  the  United  States  Naval  Observatory. 

Attest:  I-;\VD.  McPHEHSON,  Clerk. 


TABLE   OF    CONTENTS. 


Page. 

Report  of  Commodore  B.  F.  SANDS,  U.  S.  N 3 

Report  of  Professor  SIMON  NEWCOMB,  U.  S.  N.,  on  observations  of  the  eclipse,  &c.,  made  at  Des  Moiiies,  Iowa,  and 
other  places : 

General  report , 6 

Description  of  instruments 7 

Phenomena  at  first  contact 8 

Plan  of  search  for  intra-mcrciirial  planets 8 

Phenomena  of  totality 9 

APPENDIX      A.  Comparisons  of  chronometers 11 

B.  C.  Telegraphic  comparison  of  chronometer  with  Kessels  clock  beats 11 

1).  Observations  for  local  time, 12 

K.  Times  of  phases,  deduced  from  the  observations,  and  compared  with  the  tabular  times 13 

F.  Observations  of  the  duration  of  totality  and  of  other  phenomena,  by  amateur  observers 15 

I.  Near  the  northern  limit 16 

II.  Near  the  southern  limit 20 

III.  At  points  too  far  within  the  shadow  to  be  used  in  fixing  its  limits 22 

Report  of  Professor  AVu.i.iAM  HAKKNESS,  U.  S  N.,  on  observations  of  the  eclipse,  &c.,  made  at  Des  Moines,  Iowa: 

Introductory 25 

Site  of  temporary  observatory 25 

Description  of  temporary  observatory 25 

Description  of  instruments : 

Photographic  telescope 26 

Forty-three-inch  telescope 26 

Spectroscope 27 

Polariscopes 30 

Six-inch  sextant 30 

Mercurial  artificial  horizon 31 

Other  instruments  and  apparatus 32 

General  remarks  on  observations  for  time  and  latitude 32 

Observations  for  time 33 

Observations  for  latitude 37 

Telegraphic  determination  of  longitude ; 40 

Triangnlatioii  connecting  the  various  temporary  observatories 49 

Geographical  position  of  the  Court-house  Dome 58 

Height  of  the  different  stations  above  the  sea 58 

Miscellaneous  work  during  the  eclipse : 59 

Spectroscope  observations 60 

Identification  of  bright  lines 03 

Physical  constitution  of  the  corona 04 

Physical  constitution  of  red  prominences 66 

Kesults  of  spectroscope  observations 66 

Scale  of  tints 67 

Conclusion 1 67 

SCHEDULE  A.  Record  of  observat  ions  for  time  at  Des  Moines 68 

B.  Record  of  observations  for  latitude  at  Des  Moines 84 

C.  Record  of  observations  for  time  at  Washington 96 


IV  TABLE    OF    CONTENTS. 

Page. 
Report  of  Professor  J.  R.  EASTMAN,  U.  8.  N.,  ou  observations  of  the  eclipse,  &r.,  made  at  Des  Moiiies,  Iowa  : 

List  of  instruments 99 

Description  of  instrument!) : 

Telescope 99 

Actinometer 99 

Photometer 100 

Barometer  and  thermometers r 101 

Chronometers 101 

Position  of  instruments 101 

Meteorological  observations  before  and  after  August  7 , , .  102 

Observations  on  the  7th : 

State  of  the  weather , '. 103 

Phenomena  before  totality 104 

Phenomena  during  totality :  • 

Corona 104 

Protuberances 105 

Amount  of  light 106 

Observations  with  the  actinoineter,  photometer,  and  solar  thermometer 107 

Phenomena  after  totality 107 

Performance  of  actiuometer  and  photometer 108 

Performauce  of  chronometers 108 

Time , 109 

TABLE         I.  Barometer  before  aud  after  August  7 110 

II.  Dry  thermometer  before  and  after  August  7 110 

III.  Wet  thermometer  before  and  after  August  7 Ill 

IV.  Solar  thermometer  before  and  after  August  7 Ill 

V.  Weather  before  and  after  August  7 112 

VI.  Extreme  temperature  and  rain  before  and  after  August  7 114 

VII.  Mean  results  from  tables  I  to  IV,  inclusive 114 

VIII.  Results  from  observations  with  tlie  actinometer  July  29  aud  August  4 . .    115 

IX.  Results  from  observations  with  the  photometer  July  29 115 

X.  Actinometer  observations  August  7 116 

XI.  Photometer  observations  August  7 118 

XII.  Results  from  photometer  observations  August  7 119 

XIII.  Meteorological  observations  August  7 120 

Report  of  Brevet  Major  EDWARD  CUBTIS,  Assistant  Surgeon  U.  8.  A.,  ou  photographic  observations  of  the  eclipse 
made  at  Dos  Moines,  Iowa.    (Communicated  by  the  Surgeon  General  U.  S.  A.) 

I.  Synopsis  of  operations 123 

II.  The  telescope 124 

III.  The  observatory 127 

IV.  Preliminary  experiments : 

1.  Determination  of  the  chemical  focus 127 

2.  Selection  of  photographic  formulse 128 

3.  Estimation  of  length  of  exposures 129 

4.  Plan  of  operations  for  the  eclipse 131 

V.  The  eclipse -132 

VI.  The  photographs  and  their  teachings  : 

1.  Photographs  of  the  partial  phases 135 

2.  Photographs  of  the  totality 142 

VII.  Concluding  suggestions '. 151 

SCHEDULE  A.  Record  of  negatives 157 

B.  Table  showing  the  relative  actinic  force  of  the  sun  at  different  altitudes 160 

C.  List  of  articles  forming  the  equipment  of  the  photographic  expedition 162 


TABLE    OF    CONTENTS.  -v 

Page. 

Report  of  Mr.  J.  HOMKU  LANK  on  observations  of  the  eclipse  made  at  Des  Moiues,  Iowa 165 

Report  of  Mr.  W.  8.  GII.MAX.  Jr.,  on  observations  of  the  eclipse  made  at  St.  Paul  Junction,  Plymouth  County, 
Iowa  : 

Description  of  station : 

Description  of  instruments 173 

Weather  during  the  eclipse 174 

The  eclipse — first  contact 174 

Spots  on  the  sun 175 

Appearance  of  the  solar  surface 175 

Approach  of  the  total  phase 175 

Minute  crescent  near  the  sun 176 

Totality 176 

The  corona •  • - 180 

Minute  object  seen  near  the  sun 180 

Planets  and  stars  visible 181 

The  third  contact 181 

The  last  contact 181 

SCHEDULE  A-  Meteorological  record 183 

B.  Comparisons  of  chronometer  for  time 183 

Times  of  contact,  and  of  disappearance  and  reappearance  of  solar  spots 185 

Report  of  Mr.  F.  W.  BAHDWKLL,  Aid  United  States  Naval  Observatory,  on  observations  of  the  eclipse  made  at 

Bristol,  Tennessee 189 

Report  of  Brevet  Brigadier  General  AI.HKKT  J.  MYER,  Chief  Signal  officer  U.  S.  A.,  on  observations  of  the  eclipse 

made  on  White  Top  Mountain,  near  Abingdon,  Virginia 193 

Report  of  Professor  ASAPII  HALL,  U.  S.  N.,  on  observations  of  the  eclipse  made  near  Plover  Bay,  Siberia: 

Introduction 199 

Account  of  the  eclipse y 200 

Description  of  the  eclipse  by  Mr.  Rogers 201 

Mr.  Very's  letter 202 

Commander  Franklin's  letter 202 

Results  of  the  observations  of  the  eclipse 203 

Determination  of  time,  latitude,  and  longitude 203 

Latitude  of  Illionliouk 211 

Latitude  of  Duutze  Head 211 

Longitude  of  Dnntze  Head 212 

Errors  of  sextant 212 

Magnetic  observations 213 

Values  of  magnetic  force 216 

Observations  of  the  barometer  and  thermometer , 217 


LIST  OF  PLATES. 


PLATE        I.  View  of  the  temporary  observatory  at  Des  Moiues,  occupied  by  Professors  Harknesg  and  Eastmau,  and 

Dr.  Curtis. 

II.  Ground  plan  of  the  above. 
AA.  Observing  rooiu. 

a.  Door. 

666.  Shelves. 

c.  Table. 

i?.  Professor  Eastuiau's  telescope. 
f.  Professor  Harkness's  telescope. 
/.  The  equatorial  for  photography. 
;/.  Tripod  stand  for  chronometer. 
B.  Photographic  dark-room. 
hh.  Doors. 

ii.  Dumb-waiters  for  passing  plate-holders  in  and  out  of  dark-room. 
kli.  Windows,  closed  by  shutters. 
III.  Shelves. 

»i.  Trough  of  water,  holding  the  baths  for  negatives. 
«.  Trough  with  grooved  sides  for  fixing-bath. 
o.  Sink,  composed  of  a  wash-tub  with  India  rubber  waste-pipe. 
p.  Barrel  of  water,  with  pipe  and  stop-cock  projecting  through  wall  of  dark-room. 

III.  Triangulatiou  connecting  tlie  various  temporary  observatories  at  Des  Moines  in  August,  1869. 

IV.  Spectroscope  used  by  Professor  Harkness. 

V.  Spectra  of  the  corona  and  red  prominences,  observed  by  Professor  Harkness. 
VI.  Curves  showing  the  readings  of  the  barometer  and  thermometer,  by  Professor  Eastmau. 
VII.  Curves  shoiying  the  readings  of  the  wet  bulb  and  sun  thermometers,  by  Professor  Eastmau. 
VIII.  Curves  showing  the  readings  of  the  actinoineter  and  photometer,  by  Professor  Eastmau. 
IX.  Colored  drawings  of  the  totally  eclipsed  sun  as  seem  at  Des  iloines,  by  Professor  Eastman. 
X.  Fac-simile  of  Dr.  Curtis's  first  photograph  of  the  totally  eclipsed  sun  at  Des  Moines. 
XI.  Fac-simile  of  Dr.  Curtis's  second  photograph  of  the  totally  eclipsed  sun  at  Des  Moiues. 
XII.  Colored  drawing  of  the  totally  eclipsed  sun  as  seen  at  St.  Paul  Junction,  Plymouth  County,  Iowa,  by 
Mr.  Oilman. 


REPORT 


COMMODORE  B.  F.  SANDS,  U.  S.  N. 


REPORT  OF  COMMODORE   B.  l\  SANDS,  U.  S. 


UNITED  STATES  NAVAL  OBSERVATORY, 

Washington,  October  L'U,  1809. 

SlE:  In  order  that  the  Naval  Observatory  should  perform  ils  part  in  the  observations  of  the 
eclipse  of  the  7th  of  August,  of  this  year,  and  take  its  proper  share  of  duty  on  this  interesting-  occa- 
sion, which  has  engaged  the  attention  of  all  astronomers,  1  early  took  measures  towards  organizing 
parties  of  officers  from  this  observatory,  to  be  stationed  for  that  purpose  at  suitable  localities  upon 
the  path  of  totality. 

It  was  desirable  to  have  a  party  as  far  to  the  northward  and  westward  as  possible,  but  the 
uncertainty  of  the  weather  in  those  northern  regions  of  our  own  possessions  caused  me  to  hesitate 
about  detailing  one  of  our  own  officers  for  so  long  a  journey,  with  doubts  of  success  and  consequent 
loss  of  his  services  here;  but  at  the  suggestion  of  Professor  Cottin,  in  charge  of  the  United  States 
Nautical  Almanac,  that  Plover  Hay,  on  the  western  side  of  P>ehring  Strait,  would  possibly  give  a 
better  chance  for  good  observations,  and  Professor  Asaph  Hall,  United  States  Navy,  of  this  observa- 
tory, volunteering  for  the  duty,  he  was,  at  my  request,  ordered  by  the  department  to  proceed  to  San 
Francisco,  whence  one  of  onr  naval  vessels  would  take  his  party  to  such  station  at  Bchring  Strait 
as  he  might  select . 

Mr.  Joseph  A.  liogers,  of  the  Ilydrographic  OtUce,  was  detailed  to  accompany  him.  They  sailed 
from  New  York  on  the  21st  of  May,  and  arrived  at  the  station  selected  in  ample  time;  were  fully 
prepared,  and  with  every  encouragement  for  most  interesting  results,  when,  unfortunately  for  entire 
success,  the  contingency  occurred  which  1  so  much  feared,  and  the  observation  of  the  eclipse  was 
not  so  perfect  as  we  desired,  on  account  of  partial  obscuration,  at  intervals,  by  clouds,  from  just 
before  the  ingress  till  after  the  egress.  The  very  interesting  report  of  Professor  Hall  will  tell  its  own 
tale.  Valuable  results  were  obtained,  so  that  the  expedition  was  not  altogether  futile. 

Professors  Simon  Newcomb,  William  Hark  ness,  and  J.  K.  Eastman,  United  States  Navy,  were 
ordered  by  the  department,  at  my  request,  to  proceed  to  DCS  Moines,  Iowa,  and  select  such  stations 
within  one  hundred  miles  of  that  locality  as  should  be  most  suitable  for  their  separate  duties.  Pro- 
fessor Newcomb  to  observe  the  corona  and  search  for  intra -mercurial  planetoids,  according  to  his 
suggestion  in  a  paper  in  Silliman's  Journal  for  May  last ;  Professor  llarkness  with  his  spectroscope 
for  spectra]  analysis,  and  Professor  Eastman  for  meteorological  observations. 

Surgeon  General  J.  K.  Barnes,  United  States  Army,  entered  with  great  interest  into  onr  plans, 
and  kindly  detailed  Assistant  Surgeon  Brevet  Major  Edward  ( 'nrtis,  United  States  Army,  an  officer 
skilled  in  photography,  and  assistants,  to  accompany  the  observatory  party. for  the  purpose  of  pho- 
tographing the  totality  and  various  phases  of  the  eclipse. 

Vice- Admiral  Porter  kindly  loaned  the  large  equatorial  telescope  of  the  Naval  Academy  for  the 
purpose,  and  a  small  temporary  observatory  was  erected  in  our  grounds  here,  where  Dr.  Curtis 
passed  several  weeks  in  practice  and  preparation  for  his  interesting  work,  and  he  has  been  rewarded 
for  his  labor  by  photographs  which  can  scarcely  be  excelled.  The  observatory  not  having  an  instru- 
ment ready  for  reading  off  the  photographs  obtained,  that  work  wilJ  be  put  in  hand  at  once  as  soon 
as  the  instrument  is  made,  and  the  results  will  be  published  immediately. 

Upon  their  arrival  at  DCS  Moines  all  these  ollicers  selected  that  locality  as  the  best  for  their 
several  observations;  Professors  llarkness  and  Eastman,  and  Dr.  Curtis,  uniting  and  erecting  one 
observatory,  and  Professor  Newcomb  occupy  ing  another  in  a  different  part  of  the  city  for  his  observa- 
tions. 

Mr.  V.  W.  Bawlwell,  "Aid,"  was  sent  to  Bristol,  Tennessee,  for  additional  observations  upon 
the  corona,  leaving  on  duty  at  the  observatory  only  Prqiessor  Yarnall  and  Aids  Doolittle  and  Frisby. 


4  REPORT   OF   COMMODORE    SANDS. 

I  addressed  circular  letters  to  the  postmasters  on  tbe  path  of  totality  to  interest  intelligent 
observers  and  forward  their  results  to  this  observatory,  and  the  newspapers  generally  published 
our  instructions  to  observers.  From  these  reports  \ve  reap  a  good  harvest  of  information,  which, 
although  not  purely  scientific,  has  been  discussed  at  the  observatory  and  embodied  in  the  report  of 
Professor  Newcomb. 

To  do  full  justice  to  these  officers  (army  and  navy)  of  the  observatory  parties  engaged  in  these 
observations,  and  the  object  for  which  they  were  undertaken,  I  cannot  do  better  than  submit  their 
able  reports  in  full,  with  accompanying  plates  and  illustrations. 

I  have  been  favored  with  most  intelligent  and  interesting  reports  from  private  scieniilic  parties, 
which  I  append  to  this  communication.  One  of  them  is  from  Mr.  W.  S.  Oilman,  jr.,  of  New  York, 
who  has  a  small  observatory  at  the  Palisades,  and  lias  passed  his  leisure  hours  in  the  study  of 
astronomy,  making  a  specialty  of  solar  physics,  and  who,  at  his  own  expense,  witli  several  assistants, 
went  to  Iowa  to  observe  the  eclipse.  It  is  to  be  regretted  that  he  could  not  himself,  consistently 
with  his  plan  of  operations,  have  observed  with  his  large-power  telescope  the  "  star"  and  "crescent" 
reported  by  his  assistants,  who  were  not  experts  as  he  was.  The  others  are  from  .Mr.  J.  Homer 
Lane,  of  this  city,  a  gentleman  who  accompanied  the  Coast  Survey  party  of  Professor  Hilgard  to 
Des  Moines,  and  from  Brevet  Brigadier  Oeueral  A.  J.  Myer,  chief  signal  officer  United  States  Army, 
accompanied  by  Colonel  W.  Wiuthrop,  United  States  Army,  who  had  a  fine  position  on  the  summit 
of  White  Top  Mountain,  near  Abingdon,  Virginia. 

We  are  greatly  indebted  to  Mr.  William  Orton,  president  of  the  Western  Union  Telegraph  ( '0111- 
pany,  and  Mr.  Charles  A.  Tinker,  general  manager  of  the  same  company,  for  the  free  use  of  their 
telegraph  wires  on  the  evening  of  the  eclipse,  and  certain  hours  for  several  days  previously,  for  the 
exchange  of  time-signals  bet  ween  the  stations  and  our  observatory  here ;  and  also  to  .Mr.  M.  Marean, 
telegraph  operator  of  the  same  company,  who  attended  night  and  day  at  the  observatory  to  receive 
and  send  communications. 

Our  acknowledgments  are  also  due  to  the  many  amateur  observers  on  the  line  of  totality  who 
took  the  trouble  to  send  us  their  observations,  from  which  we  have  gleaned  much  information  that 
is  serviceable  in  our  reports. 

I  have  the  honor  to  be,  very  respectfully,  your  obedient  servant, 

B.  F.  SANDS, 
Commodore,  Superintendent. 
Hon.  GEO.  M.  KOBESON, 

Secretary  of  the  Navy,  Washington 


REP  OIR  T 


PROFESSOR  SIMON  NEWCOMB,  U.  S.  N 


REPORT   OF    PROFESSOR   NEWCOMB,  U.  S.  N. 


UNITED  STATES  NAVAL  OBSERVATORY, 

Washington,  September  20,  1809. 

SIR  :  I  liave  the  honor  to  present  the  following  report  of  my  observations  on  the  total  eclipse 
of  August  7th  last. 

In  obedience  to  the  orders  of  the  department  and  of  yourself,  I  left  Washington  on  July  28th, 
and  arrived  in  Des  Moines  on  the  31st.  I  took  with  me  the  following  instruments : 

The  observatory  comet-seeker,  of  four  inches  aperture,  equatorially  mounted. 

The  object-glass  of  the  transit  circle,  aperture  eight  and  one-half  inches,  focal  length  twelve 
feet  one  inch. 

The  object-glass  of  the  refraction  circle,  aperture  six  inches,  focal  length  about  nine  feet. 

A  Gambey  sextant  from  the  Hydrographic  Office,  reading  to  ten  seconds  of  arc,  with  artificial 
horizon. 

Mean-time  chronometer,  Negus  No.  12S 1 . 

On  my  arrival  I  found  the  temporary  wooden  mounting  for  the  extra  object-glasses,  which  you 
had  directed  Professor  Harkness  to  have  made,  quite  ready  for  me.  They  were  of  the  following 
construction  :  Two  pieces  of  8"  by  8"  timber  were  firmly  set  in  the  ground  to  the  depth  of  three  feet, 
the  distance  between  them  being  twenty-seven  inches.  A  strong  frame,  of  two-inch  stuff,  twenty- 
seven  inches  long,  passed  between  them,  turning  on  a  horizontal  axis.  Through  the  center  of  this 
frame  passed  the  substitute  for  the  telescope  tube,  consisting  of  a  box  twelve  inches  square  and 
twelve  feet  long,  blackened  on  the  inside  and  open  at  both  ends.  The  object-glass  was  fastened  into 
one  end,  the  eye-piece  into  the  other.  It  turned  in  the  frame  on  an  axis  at  right  angles  to  the  other 
axis,  but  admitting  of  a  motion  of  only  about  twenty-five  degrees  on  each  side.  Connecting  rods 
pass  from  near  the  bottom  of  each  post  to  near  the  eye-end  of  the  telescope,  where  they  could  be 
clamped  with  a  button,  and  the  telescope  thus  be  fixed  in  any  required  position. 

If  1  had  the  eclipse  to  observe  over  again  I  should  try  to  make  the  mounting  an  equatorial  one, 
by  pointing  the  axis  of  the  frame  towards  the  pole. 

After  an  examination  of  different  localities  I  selected  as  my  observing  station  a  point  in  the 
yard  of  the  county  court-house,  near  the  Coast  Survey  longitude  station.  It  is  nearly  a  mile  south, 
and  nearly  1s  west  of  Professor  Harkness's  observatory. 

From  data  obtained  privately  from  other  parties,  I  concluded  that  the  position  of  my  station 
was  very  nearly  as  follows : 

Latitude 41°  35'  4" 

West  longitude  from  Washington I1'  Gm  178.0; 

a  result  which  I  do  not  think  can  be  in  error  by  as  much  as  2"  in  latitude,  or  1s  in  longitude. 

The  occupation  of  a  station  near  my  lodgings  and  near  workshops,  stores,  &c.,  saved  much 
trouble  and  expense.  It  is  just  to  state  that  it  was  only  through  official  courtesies  rendered  by  the 
following  gentlemen  that  1  was  enabled  successfully  to  occupy  a  station  so  convenient,  namely,  his 
honor  J.  II.  Hatch,  mayor  of  Des  Moines,  his  honor  J.  li.  Miller,  judge  of  the  county  court,  and 
Hoyt  Sherman,  esq. 

A  position  was  chosen,  such  that  the  gable  end  of  the  court-house  could  be  used  in  mounting 
the  screens.  A  horizontal  arm  was  made  to  project  several  feet  to  the  north  of  the  roof.  On  this 
arm  were  mounted  three  circular  screens  of  15,  18,  and  21  inches  diameter,  in  such  a  position  that 
they  would  just  hide  the  sun  from  points  near  the  south  end  of  my  observatory  during  the  total 
eclipse.  Their  diameters  as  measured  with  a  sextant  from  the  observatory  were  respectively  33', 


8 


REPORT   OF   PROFESSOR   NEWCOMB. 


39',  and  46',  the  largest  one  being  farthest  out.  The  comet-seeker  was  mounted  near  the  south  end 
of  the  observatory,  so  that  the  outer  screen  could  be  made  to  hide  the  corona  by  sliding  it  out.  Xext 
to  the  north  was  the  transit-circle  glass,  and  then  the  0  inch  glass.  The  observatory  consisted  only 
of  four  walls  of  rough  boards  to  protect  the  observers  against  intrusion  and  the  instruments  from 
the  wind. 

In  mounting  the  instruments  I  was  altogether  without  assistance  except  that  of  the  carpenter 
and  of  occasional  volunteers,  curious  to  see  the  inside  of  our  walls.  On  Thursday,  however,  I  pro- 
cured through  Professor  Safford  the  assistance  of  Mr.  Armstrong,  a  student  in  the  University  of 
Chicago,  whose  zeal  and  alacrity  rendered  his  services  very  valuable.  I  also,  as  authorized  by  you. 
tendered  the  use  of  my  wooden  telescopes  to  Professor  John  Fraser,  president  of  the  University  of 
Kansas,  and  Mr.  J.  II.  Lane,  of  Washington,  the  former  taking  the  transit  glass,  the  latter  that  of 
the  refraction  circle.  I  requested  them  to  make  their  reports  directly  to  yon.  Mr.  Armstrong  beat 
the  seconds  at  the  chronometer,  counting  every  tenth  one  aloud. 

During  the  two  days  preceding  the  eclipse  the  heavens  were  covered  with  clouds,  brought  on 
by  an  east  wind,  and  on  Friday  there  was  inist  enough  to  make  the  ground  in  our  iuclosure  too 
muddy  for  convenience.  On  Saturday  morning  the  clouds  cleared  away,  leaving  a  dense  haze.  This 
haze  grew  thinner  in  the  course  of  the  day,  but  did  not  entirely  vanish. 

In  observing  the  contacts  1  used  the  comet-seeker  with  an  aperture 
reduced  to  one  inch,  a  power  of  40,  and  a  yellow  shade.  As  thus  seen, 
the  definition  of  the  limb  was  very  fine.  The  eye-piece  was  furnished 
with  four  coarse  black  bands,  arranged  as  in  the  margin,  with  a  pair 
of  fine  spider  lines  between  them.  Turning  the  ocular  twenty  degrees 
from  the  position  in  which  the  sun  traveled  along  the  wire,  the  point 
of  the  liinb  where  the  first  contact  was  to  take  place  was  parallel  to 
one  set  of  wires,  and  I  thus  knew  exactly  where  to  look. 

At  chronometer  time 


I  saw  the  minutest  visible  notch  exactly  at  the  expected  point  of  contact.  For  two  or  three  seconds 
I  was  in  some  doubt  whether  it  was  really  the  moon's  limb ;  but  in  three  seconds  more  the  limb  first 
above  and  then  below  the  notch  began  to  assume  the  sharp,  rough  character  peculiar  to  the  moon's 
limb,  and  left  no  doubt  on  the  subject.  As  the  first  part  of  the  moon  which  impinged  on  the  sun 
was  a  quite  prominent  mountain,  I  think  the  time 

9h  5G"'  38.5 

may  be  taken  as  the  time  at  first  contact  of  the  general  contour  of  the  moon  with  that  of  the  sun, 
as  it  resulted  from  my  observation.  But  the  observation  at  2s.O  was  very  precise  and  satisfactory. 
In  about  five  minutes  from  the  commencement  I  placed  one  set  of  wires  parallel  to  the  line  of 
cusps,  and  noted  the  moment  at  which  the  line  of  cusps  extended  between  the  internal  edges  of  the 
other  thick  wires.  This  took  place  at  chronometer  time 

10h  I-1  31s 
an  observation  of  which  I  felt  sure  within  a  second. 

The  space  thus  measured  by  the  cusps  was  soon  afterward  determined  by  transits  of  the  sun's 
limb  over  it. 

Coming  now  to  the  preparations  for  total  phase,  I  remark  that  the  main  object  I  kept  in  view 
was  to  determine  whether  there  was  anything  at  all  visible  outside  the  usually  assigned  limits  of 
the  corona,  and  yet  so  near  the  sun  as  to  be  invisible  at  other  times.  More  especially  was  it  determ- 
ined to  search  in  the  neighborhood  of  the  sun  for  an  immense  group  of  very  minute  intra-inercurial 
planets,  the  existence  of  which  had  been  rendered  so  probable  by  the  researches  of  Le  Verrier  on 
the  motion  of  Mercury.  In  making  this  search  my  plan  was  to  set  two  of  the  telescopes — the  8" 
and  4" — in  known  directions,  by  pointing  each  of  them  on  the  sun  at  some  definite  moment,  ten  or 
fifteen  minutes  before  the  commencement  of  totality,  and  immediately  after  the  latter  phase  to  make 
a  map  of  any  objects  that  might  be  seen  in  either  field  of  view ;  then  to  move  the  telescope  into  dif- 
ferent positions  and  count  the  objects  in  each  field  of  view. 


OBSERVATIONS    OF    THE    ECLIPSE    OP    AUGUST    7,    J869.  9 

After  thus  sotting-  the  telescopes,  and  removing  the  caps  and  colored  glasses,  I  got  into  a 
nearly  dark  box,  requesting  President  Fraser  to  call  when  he  saw  the  sunlight  was  just  about  to 
disappear. 

A  minute  or  two  before  the  advent  of  darkness  a  crowd  of  people  who  had  taken  their  position 
on  the  roof  of  the  court-house  greeted  the  progress  of  the  phenomenon  with  loud  and  prolonged 
cheering,  rendering  me  quite  uneasy  for  our  time  observations.  But  I  think  they  grew  quite  silent 
before  the  sun  had  entirely  disappeared,  and  did  not  renew  their  cheers  on  its  reappearance. 

I  emerged  from  the  box  a  few  seconds  before  total  darkness,  but  did  not  look  up  until  Professor 
Fraser  had  given  me  the  word.  I  then  took  a  single  glance  at  the  corona  through  two  thicknesses 
of  green  glass.  I  then  attempted  to  hide  the  corona  behind  the  outer  and  the  larger  of  the  screens, 
and  thought  I  had  done  so,  but  after  the  total  phase  had  passed  I  was  convinced  that  I  had  mis- 
taken the  moon  itself  for  the  screen.  Though  I  knew  theoretically  that  the  sky  in  the  direction  of 
the  moon  ought  to  seem  darker  than  that  outside  of  the  corona,  I  was  wholly  unprepared  for  so 
strong  an  illusion  of  a  black  globe  hanging  in  mid-air.  The  corona  itself  was  far  less  bright  than 
I  had  anticipated.  I  then  looked  most  carefully  along  the  direction  of  the  ecliptic  to  ascertain 
whether  then;  was  ;in,v  appearance  of  a  blush  of  light  extending  out  in  that  direction,  but  I  could 
not  perceive  the  faintest  trace  of  any. 

I  next  went  in  succession  to  the  two  telescopes,  but  not  an  object  was  visible  in  either.  I  then 
swept  somewhat  at  random,  but  near  the  ecliptic  with  the  comet-seeker,  without  finding  anything. 
As  any  isolated  object  I  might  find  would  not  only  be  incapable  of  certain  identification,  bat  would 
fail  to  fulfill  the  condition  of  accounting  tor  the  motion  of  the  perihelion  of  Mercury,  I  could  only 
regard  further  search  as  useless,  and  therefore  proceeded  to  the  study  of  the  corona.  But  1  first 
took  a  general  view  of  the  phenomenon  through  the  comet-seeker,  with  the  full  aperture  and  no 
screen.  Nearly  or  quite  the  entire  corona  was  then  visible  at  a  single  view.  As  thus  seen,  I  regret 
that  I  can  describe  it  with  no  more  accuracy  than  as  an  effulgence  which,  while  not  at  all  dazzling 
to  the  eye,  was  yet  glorious  beyond  description.  An  immense  protuberance  on  the  upper  side  of 
the  inverted  corona  attracted  my  attention.  During  the  hurried  inspection  1  made  of  it,  the  follow- 
ing points  were  noticed : 

1.  It  did  not  seem  materially  brighter  than  the  corona;  it  could  be  viewed  directly  without  the 
eye  being  at  all  dazzled. 

2.  The  large  predominance  of  red  in  its  color  was  so  evident  and  so  strongly  marked  that  I 
could  not  entertain  a  doubt  of  its  reality.     The  tint  was  a  most  beautiful  pink. 

.'5.  Its  structure  was  not  uniform,  nor  did  the  protuberance  bear  the  slightest  resemblance  to  a 
name.  It  looked  like  an  immense  pile  of  cumulus  clouds,  illuminated  by  a  white  and  red  sun,  and 
thus  exhibiting  different  shades  of  color  as  the  light  from  the  one  sun  or  the  other  chanced  to  pre- 
dominate at  different  points. 

Leaving  the  telescope,  I  returned  to  naked-eye  observations.  Looking  directly  at  the  corona, 
there  was  no  actual  appearance  of  striation,  but  it  seemed  to  be  of  a  jagged  outline,  extending  out 
into  four  sharp  points,  nearly  in  the  horizontal  and  vertical  direction,  while  midway  between  these 
points  the  serrated  edge  hardly  seemed  to  extend  beyond  the  body  of  the  moon.  The  greatest  dis- 
tance to  which  the  extreme  points  seemed  to  extend  did  not  exceed  a  semi-diameter  of  the  moon, 
and  there  was  nothing  like  long  rays  of  light  extending  out  in  any  direction  whatever.  When  I 
turned  my  head,  the  points  did  not  seem  to  turn  with  it.  Still,  I  experienced  a  singular  difficulty 
iu  judging  accurately  either  of  the  number  or  direction  of  the  jagged  points,  or  of  the  extent  to 
which  they  might  be  optical  illusions,  produced  by  the  differences  in  the  height  and  brilliancy  of 
different  parts  of  the  corona. 

The  green  glass,  however,  settled  the  latter  question.  Seen  through  this  medium  the  corona 
consisted  simply  of  four  or  five  prominences,  extending  around  the  moon,  smooth 
in  their  outline,  shading  off  by  imperceptible  gradations  and  rising  to  different 
heights,  the  greatest  height  not  exceeding  four  or  five  minutes.  The  accom- 
panying sketch  gives  a  general  idea  of  the  impression  produced  by  the  view 
through  the  colored  glass,  but  must  not  be  taken  as  a  drawing  of  the  actual  phe- 
nomenon. I  have  no  doubt  that  the  serrated  appearance  of  the  corona  and  the 
pointed  rays,  were  purely  optical  results  of  the  irregular  heights  of  the  prominences.  A  fish-tail 

2* 


10  REPORT   OF   PROFESSOR   NEWCOMB. 

gas-light,  seen  against  a  dark  ground  at  a  distance  of  fifty  yards  or  more,  presents  to  my  eye  a  simi- 
lar appearance. 

I  observed  the  end  of  totality  with  the  naked  eye  at 

11"   1"'  2G* 

chronometer  time.  Mr.  Armstrong  had  continued  the  counting  and  beating  of  the  chronometer 
seconds  through  the  entire  period  of  totality,  without  once  raising  his  eyes  from  the  chronometer. 
The  reappearance  of  sunlight  was  preceded  by  a  general  illumination  of  the  atmosphere,  commenc- 
ing three  or  four  seconds  before  the  actual  blazing  forth  of  the  sun. 

Two  or  three  minutes  before  the  end  of  the  eclipse,  at  [llh  57'"]  -.'!s  chronometer  time,*  the 
chord  of  cusps  measured  a  space  between  one  fine  middle  wire,  and  an  edge  of  one  parallel  coarse 
wire  which  had  been  found  to  be  passed  over  by  the  sun  in  27S.1.5,  a  mean  of  four  observations. 

The  last  contact  I  observed  at  1 11'  .~>S'"  i>4s.5. 

The  outline  of  the  moon  was  quite  smooth  and  regular  near  the  point  of  last  contact. 

Accompanying  this  report  are  the  following  papers,  which  I  respectfully  request  may  be  con- 
sidered as  forming  part  of  it : 

A.  Comparisons  of  my  chronometer  witli  those  of  other  parties  engaged  in  observations  of  precision. 

The  comparisons  were  made  in  order  to  have  as  many  connections  as  possible  with  the  work  of 
other  independent  observers. 

B.  Comparisons  of  chronometer  with  the  (vessels  clock  at  Washington  on  the  evening  (if  the  eclipse. 

the  clock  sending  its  beats  by  telegraph. 

C.  A  similar  comparison  made  by  sending  signals  to  Washington  contemporaneously  with  certain 

beats  of  the  chronometer.     The  signals  are  fouud  on  the  chronograph  sheet  of  August  7. 

D.  Observations  with  a  (lambey  sextant  to  obtain  the  error  of  the  chronometer  on  local  time. 

E.  Times  of  the  phases  concluded  from  my  observations,  anil  compared  with  those  computed  from 

the  tables. 

F.  Summary  of  observations  for  the  duration  of  totality  at  various  points  near  the  limits  of  the 

shadow,  made  in  pursuance  of  the  circular  of  instructions  sent  out  by  you,  and  collected  from 

the  reports  placed  in  my  hands. 

On  these  observations  I  beg  leave,  to  remark  that  both  their  number  and  apparent  precision 
exceed  what  we  had  reason  to  expect.  One  of  my  fears  in  proposing  the  plan  was  that  we  should 
have  manufactured  observations  sent  us,  but  there  are  none  that  I  can  detect  as  such.  The  dis- 
cordance between  the  number  made  near  the  northern  and  southern  limits  is  much  to  be  regretted. 
Those  made  will,  however,  I  conceive,  suffice  to  fix  an  apparent  relative  co-ordinate  of  the  sun  and 
moon  within  a  small  fraction  of  a  second  of  arc. 

This  report  having  been  long  delayed  by  illness,  it  may  not  be  improper  to  state  that  I  have  in 
the  mean  time  carefully  avoided  acquiring  any  knowledge  of  the  descriptions  of  other  witnesses  of 
the  eclipse  which  could  affect  my  impressions  of  the  optical  portion  of  the  phenomena. 

Very  respectfully,  your  obedient  servant, 

SIMON  NEWCOMB, 

Professor  Mathematics,  U.  8.  N. 
Commodore  B.  F.  SANDS,  U.  S.  N., 

Superintendent  of  U.  8.  Naval  Observatory. 

"The  hours  and  minutes  are  assumed,  not  having  been  observed. 


OBSERVATIONS    OF    THE    ECLIPSE    OF   AUGUST    7,    1869.  11 

A. — Comparisons  of  cltninoim  -ti-r  \i'i/nn  li'Sl  iritli  other  chronometers  at  Des  Moines. 


Date. 

Face   of  Ne- 
gns  12*1. 

Face  of  chro- 
nometer. 

Chronometer. 

Possessor   of  chro- 
nometer. 

1869. 

July    31.2 

9     7  59.  3 

9  11     0 

Negus  1300      . 

Professor  Harkuess. 

9     9  50.  4 

9  15     0 

Negus  1319      . 

Professor  llarkuess. 

Aug.      0.9 

4  32  40.0 

4  37  50 

Negus  1319   '  . 

Professor  llarkuess. 

1.9 

4  44  49.11 

4  50     0 

Negus  1319      . 

Professor  llarkness. 

4.0 

9  22  40 

9  27  52.  4 

Negus  1319      .       Professor  llarkuess. 

{2    2  50 

7  50  54.8"| 

Karr,  in.  t.,     ^ 

Mr.  E.  Qoodfeliow, 

6.8 

2     3    5 

7  51   10.  5  I 

2     3  16 

7        21.  2  j 

(pocket.)       ) 

1'.  S.  Coast  Survey. 

7.0 

(   7  34  30 
t   7  35     5 

2  37  59.0^ 
2  38  34.  5  > 

Chronometer  } 
watch.         ) 

Mr.  White. 

7.2 

t    0  16  20 

7  20    7.2) 

Chronometer  f 

Mr.  White. 

<    0  17     0 

7  20  47.  0  $ 

watch.          ii 

7.2 

11   51  30.5 

4     0  50.  0 

Fletcher  1?0r 

Mr.  J.  E.  Hilgarcl. 

7.4 

3  28  49.  5 

6  22  40 

Kessels  12*7 

Mr.  J.  E.  Hilganl. 

7.  1 

4  10    2.5 

740 

Kessels  12*7          Mr.  J.  E.  Ililganl. 

B. — CoiHiHirixoHx  ofXcyux  1  ->sl  iritli  A'c.v.s-r/.v  <-lo<-k  hciilx,  tin  xcntfroiu  Waxhi at/ton  Inj  teleffraph^on  Aug. 7.3. 
Double  beats,  marking  beginnings  of  minute,  were  received  at 

/I.  HI.  S, 

"2  L'4  43.9 

11  25  43.7 

12  L>f>  43.5 
2  27  43.4 
2  31  42.7 


It. 


Coincidences  of  beats  at 


m. 

2        2G 

30 


50: 
0. 


C. — Times  of  reception  of  5 -second  signals  at  Washington,  sent  from  De,t  Moines  in  coincidence  irith 

certain  beats  of  chronometer  Negus  1281.     . 


Mean 

Correction  of  clock 


Chronometer. 

ft. 

m. 

8. 

3 

7 

50 

55 

8 

0 

50 

55 

9 

0 

5 

15 

20 

25 

30 

55 

10 

0 

3 

9 

0.0 

Time  by  Kessels  clock. 

ft. 

»i.       a. 

19 

8     13.7 

18.7 

23.fi 

9     13.8 

18.8 

23.8 

28.8 

38.9 

43.9 

48.8 

53.9 

10     19.1, 

24.0 

19 

9    23.83 

—  27.17 


12 


REPORT   OF   PROFESSOR  NEWCOMB, 


D. — Double  altitudes  of  the  sun's  limb,  observed  tcith  Gambey  se.rtant  by  reflection  from  mercury,  at 
the  Court-house,  Den  Moines,  tcith  readings  of  sextant  for  tangency  of  limbs  of  sun,  to  give  inilc.r 
error,  and  the  concluded  results  of  the  observations. 


READINUS   lot!   INDEX   KliROIi. 


Date. 

Off  limb. 

On  limb. 

Remarks. 

O             '          " 

c      /        // 

Aug.  2.  0 

359    27    50 

0    32      0 

359    28    15 

0    31     30 

Before  observing  altitude*. 

4.2 

359    28    10 

0    31     10 

After  observing  altitudes. 

6.9 

•     359    27    50 
359    27    30 

0    31      5  ) 

o    30    r,o  } 

After  observing  altitudes, 

7.9 

359    28     10 
359    28     10 

0     31     25  I 
0     31       5  J 

After  observing  altitudes. 

8.2 

359    27     30 
359    27    30 

0     30     40  ? 
0     30     45  $ 

After  observing  altitudes. 

Date. 

Time  by 
chronometer. 

Reading  of 
sextant  for 
double  alt. 

Sun's 
limb. 

Chronometer 
fast  of  appa- 
rent time. 

Remarks. 

1869. 

/I.    m.      ». 

o     /     // 

It.   III.         8. 

Aug.  3.  8 

1  29  42.0 

49  24  35 

U. 

6  18  52.5 

Adopted  index  cor.  -f  10". 

31  27.0 

50    3  30 

U. 

53.0 

It.   HI.       X. 

33  20.  5 

50  45  55 

U. 

52.9 

Mean            6  18  52.  4 

34  56!  5 

51  21  45 

U. 

52.9 

Eq.  of  time       ....     —        5  47.  5 

36  14.5 

50  48    5 

L. 

52.  1 

Mean  time  error    ...          6  13    4.  9 

37  17.0 

51  11  25 

L. 

51.7 

38  30.5 

51  38  40 

L. 

52.7 

39  21.  0 

51  57  55 

L. 

51.5 

Aug.  4.  2 

10  38  41.7 

59    9  20 

L. 

6  18  47.7 

Adopted  index  cor.  -)-  14". 

40  35.5 

58  27    5 

L. 

48.1 

It.  in.     8. 

42  10.  5 

58  54  15 

\\ 

46.  5 

Mean                                                6  18  47.8 

43  19.  5 

58  29     0 

u! 

48.  1 

KII   time      -                             —        5  45.5 

44  39!  5 

57  59  10 

u. 

48!  3 

Mian  time  error    ...           6  13    2.3 

46  15.0 

56  23  30 

L. 

(56.  5) 

Probably  T.  limb,  with  a  mistake  of  1° 

47  43.0 

56  50  50 

U. 

48.8 

iu  the  record.    The  corrected  error  is 

49  33.5 

56    9  20 

U. 

47.9 

then  6h  18m  47".  9. 

• 

50  54.  5 

55  38  45 

U. 

46.9 

Aug.  6.  9 

3  42  48.  0 

95  48    0 

L. 

6  18  29.  6 

Adopted  index  cor.  -|-  42". 

44  47.2 

96  28    5 

L. 

30.0 

h.  m.    «. 

45  46.  5 

96  48    0 

L. 

30.  1 

Mean                      ...          6  18  29.  9 

46  58.  0 

97  12  30 

L. 

28  0 

Eq  time            -           -     .     —        5  27.  9 

48  35!  0 

97  44  40 

L. 

29!  0 

Mean  time  error    ...          6  13    2.  0 

50  40.  0 

99  28  50 

U. 

30.8 

51  35.5 

99  47  35 

U. 

29.9 

52  37.  0 

100    7  45 

U. 

30.6 

53  31.2 

100  25  30 

U. 

31.2 

54  43.0 

100  49  30 

U. 

29.7 

Aug.  7.  9 

2  59    4.  5 

80    9  35 

L. 

6  18  22.  5 

Adopted  index  cor.  +  18". 

3    0  53.  7 

80  49    0 

L. 

21.5 

A.  »H.      S. 

2  Tfi  1 

81  26    2 

L. 

21.2 

Mean                                            6  18  22.  2 

-     •  "  '.  O 

4.    5.5 

81  57  35 

L! 

22  6 

Eq.  time      —        5  20.  7 

5  49!  7 

82  34  50 

L. 

22.2 

Mean  time  error    ...          6131.5 

7  56.7 

84  23  15 

u. 

23.2 

9  11.6 

84  49  55 

U. 

22.8 

12  21.5 

85  57  30 

U. 

22.7 

13  31.5 

86  22  41 

U. 

21.5 

14  26.5 

86  41  50 

U. 

22.2 

Aug.  8.  2 

10  16  32.  0 

66  50  50 

U. 

6  18  16.6 

Adopted  index  cor.  +  54". 

17  51.5 

66  21  40 

U. 

17.5 

/i.  m.    8. 

MI    fi  u 

65  54  40 

U. 

20.  1 

Mean                                 '.          6  18  17.5 

A*7       U.  O 

20  49.  5 

65  15  25 

u' 

16  6 

Eq  time                                 •           5  18.  3 

22    o!s 

64  «  55 

u! 

ie!i 

Mean  time  error    ...          6  12  59.  2 

23  48.5 

63    5  55 

L. 

17.0 

24  57.0 

62  40  55 

L. 

17.7 

25  50.  0 

62  21    5 

L. 

17.8 

26  49.5 

61  59  10 

L. 

18.0 

27  49.7 

61  36  40 

L. 

18.0 

OBSERVATIONS   OF    THE    ECLIPSE    OP   AUGUST   7,    1869.  13 

E.  —  Times  of  jiltftxt'x  ili'ilmnl  J'nun  ulixir  rut  ions,  and  compari'il  ir'itli  the  tabular  times. 


From  the  preceding  exhibit  (D)  it  will  be  seeu  that  the  general  rate  of  the  chronometer  is  about 
(iiS.s  per  day,  losing.  Also,  there  are  two  days  on  which  altitudes  were  observed  both  iu  the  fore- 
noou  and  afternoon,  namely,  August  4  and  August  8.  Correcting  the  observed  errors  for  rate  of  the 
chronometer,  it  seems  the  forenoon  errors  exceed  the'afternoon  errors  by  the  following  amounts  : 

8. 

August  4,     2.3 
8,    2.1 

Mean  2.2 

This  difference  probably  arises  from  eccentricity  of  the  sextant,  leading  to  the  observed  alti- 
tudes being  constantly  too  great.  In  the  absence  of  any  certain  knowledge  of  its  law  we  shall  divide 
the  effect  equally  between  the  observed  errors  by  applying  —  I'M  to  the  forenoon  errors  and  +  1.M 
to  the  afternoon  errors  to  obtain  the  concluded  error.  Thus  the  following  errors  are  obtained  : 

7l.         m.  K. 

August  4.0,     G     1.3    3.6 
6.9,  0.9 

8.0,  0.4 

They  give  for  the  error  on  local  time  on  the  afternoon  and  evening  of  August  8  : 

G"  13"'  0s.  7. 

The  error  of  the  chronometer  on  Washington  time  may  be  obtained  with  great  precision  from 
the  data  in  Kxhibits  B  and  ('.  From  .15  we  find,  knowing  the  longitude  to  be  about  I1'  G1"  17s,  and 
the  Washington  clock  to  be  27s  fast  of  sidereal  time  : 

/i.      m.      s.  It.       HI.        s. 

2  30    0  chron.  =  18    30    17,     Kessels  clock. 

=  18    29  49.8,  Washington  sidereal  time. 

=  10      2  15.8,  Washington  mean  time. 
Whence  chronometer  fast  of  Washington  time: 

.V'  G1"  44".2. 
Again,  from  C  we  find 

/i.       in.    s.                       It.      in.  s. 

3  9    0  chrou.  =  19      9  23.8,  Kessels  clock. 

=  19      8    56.6,  Washington  sidereal  time. 
=  10      2    16.2,  Washington  mean  time. 
Whence  chronometer  fast  of  Washington  time: 

5"  G"'  43S.8. 

The  difference  of  Os.4  or  08.43  when  the  second  decimal  of  seconds  is  included,  is  attributable 
to  the  time  of  transmission  of  the  galvanic  current  through  two  thousand  four  hundred  miles  of 
wire,  to  armature  time,  and  personal  error  of  the  observer  in  sending  signal. 

The  concluded  error  of  chronometer  on  Washington  mean  time  is  therefore, 

5"  Gm  448.0. 

Comparing  this  result  with  the  error  of  chronometer  on  local  time,  we  have  for  the  longitude 
of  Des  Moines  Court-house  : 

I1'  Gm  1GS.7.       . 

The,  definitive  error  on  local  lime  will  be  obtained  by  applying  to  the  Washington  time  the 
longitude  resulting  from  the  combination  of  my  own  determinations  with  those  of  Professor  I  lark- 
ness.  The  geodetic  difference  of  longitude  between  the  Court-house  and  Professor  Harkness's 
observatory  is  Os.7.*  The  longitude  of  the  latter,  resulting  from  his  observations,  being  I'1  G'"  I  6s.  I  . 
gives  for  that  of  the  Court-house  I1'  G1"  1GS.8.  This  result  is  the  mean  of  five  observations.  This 
*  It  may  be  deduced  from  the  <lat:i  of  these  reports  that  from  the  comparison  of  chronometers,  made  on  August  4, 
will  result  the  difference  0".6. 


14 


REPORT    OF   PROFESSOR   KEWCOMB. 


differs  only  Os.l  from  my  single  determination  on  August  7,  and  will  therefore  be  adopted.     We 
have,  therefore,  for  the  error  of  chronometer  in  local  time : 

61'  13'"  08.8. 

Applying  these  corrections  to  the  observed  times  of  the  three  phases,  we  have  the  following 
results,  which  are  compared  with  those  computed  from  the  data  of  the  American  Ephemeris : 


• 

Local  time. 

Washington 

time. 

Ccllnp. 

time. 

Error  of 

(allies. 

Error  in 
arc. 

It.      III.            8. 

7i.    m.       H, 

». 

8, 

ii 

First  contact  .     .     . 

3    43      -2.  1 

4     49    1'J.  5 

7.0 

]•>..-> 

6.0 

End  of  totality    .     . 

4    48    25.2 

5    54      2.0 

31.6 

10.  1 

5.4 

Last  contact  . 

5    45    23.7 

6    51     40.5 

32.7 

7.8 

4.4 

Besides  these  phases  we  have  two  measured  chords,  oue  just  after  the  beginning  of  the  eclipse, 
the  other  just  before  the  end.  The  observations  may  be  expressed  as  follows:  at  10b  lm  31s  chro- 
nometer, the  length  of  the  chord  was  equal  to  the  space  passed  over  by  the  sun  by  its  diurnal  motion 
in  548.55.  At  [llh]  [57m]  238  it  was  equal  to  the  space  passed  over  in  27S.15. 

These  observations  were  reduced  in  the  following  way :  represent  by  s  the  half-length  of  the 
measured  chord,  put  r  and  r'  for  the  apparent  semi-diameters  of  the  sun  and  moon  as  seen  by  the 
observer,  and  D  for  the  apparent  distance  of  their  centers.  Then 

D  =  Vr^^fz  +  Vr'*  —  s2 
or,  if  we  put 

* 

sm  a  =  - 
r 


sin  a'= 


r' 


we  have 

D  =  »'  COS  a  -4-  r'  COS  a' 

This  is  the  distance  deduced  from  observations.  The  distance  was  calculated  from  the  tables 
for  the  same  absolute  time  by  applying  the  parallax  in  right  ascension  and  declination  to  the  geo- 
metric co-ordinates.  Thus  was  found — 


Greenwich 

Observed 

Tabular 

Krriir  of 

time. 

distance. 

distance. 

tables. 

7i.    m.       s. 

/         // 

/         // 

// 

9    57     19.0 

. 

32    23.3 

. 

10      2    59.0 

29    37.3 

29     39.3 

+  2.0 

11     58    51.0 

31    38.  3 

31     47.  \ 

+  8.8 

The  two  errors  ought  to  have  opposite  signs,  so  that  there  is  a  discrepancy  of  nearly  11"  in  the 
results.  There  appears,  therefore,  to  be  some  abnormal  error  in  the  data  which  1  cannot  account 
for,  as  the  observations  were  carefully  made,  and  seemed  to  me.  very  reliable.  No  correction  has 
been  applied  for  the  effect  of  refraction.  At  the  actual  altitudes  of  the  sun  it  would  be  quite  small. 
and  would  tend  to  increase  the  discrepancy. 

The  first  of  the  above  times  is  that  of  the  first  contact  as  computed  from  the  data  of  the  Amer- 
ican Ephemeris.  The  distance  of  centers  was  computed  to  see  whether  it  would  agree  with  the  sum 
of  the  semi-diameters.  The  difference  is  0".3. 

Using  only  contacts,  and  neglecting  the  effect  of  the  possible  error  of  the  moon's  latitude,  which 
is  probably  small,  we  have  the  following  results  for  the  relative  errors  of  the  lunar  and  solar  tables : 

Peirce's  3)  — Hansen's  ©  too  great  by  5".3. 
Hanseu's  3> — Le terrier's  ©  too  great  by  2". 7. 


OBSERVATIONS   OF   THE    ECLIPSE   OP   AUGUST   7,    1869.  15 

The  last  result  is  deduced  from  the  fact  that  in  the  British  Nautical  Almanac  the  moon's  longi- 
tude is  l".fl  less,  and  (lie  sun's  1".0  greater  than  in  the  American  Ephemeris: 

F. — Obtterrtttionx  oftlic  <litr«li<»i  of  totality  and  of  other  phenomena  made  by  amateur  observers. 

Most  of  these  observations  were  made  iu  pursuance  of  a  request  accompanying  a  circular  of 
instructions  of  which  the,  following  is  a  copy  : 

IXSTIUX TIOXS  mi!  mi:  OHSFU\ •  \TION  OF  THE  TOTAL  ECLIPSE  OF  AUGUST  7,  1869,  HY  OBSEHVEKS  WITHOUT  TELESCOPES 

NEAR  THE  LIMITS  OF  TOTALITY. 

The  following  information  is  desired  by  the  United  States  Naval  Observatory,  namely:  The  duration  of  total  eclipse 
at  raritiH*  jilitn1*  iiliinii  tlie  liuf  of  totality,  situated  between  one  and  ten  miles  from  its  limit*. 

To  obtain  this  information  the  observatory  invites  the  co-operation  of  intelligent  citizeus  residing  near  the  limits, 
and  the  following  instructions  are  prepared  tor  the  use  of  those  who  will  co-operate: 

Imtti'iiments. — The  only  indispensable  instrument  is  a  good  watch, provided  with  asecond  hand,  and  having  a  white 
face.  The  minute  hand  should  be  carefully  set,  so  as  to_be  on  an  exact  minute  when  the  second  hand  is  at  GO".  This 
being  done  it  is  no  matter  how  tar  wrong  the  watch  may  be.  A  good  auxiliary  w  ill  be  a  common  spy-glass  lashed  to  a 
round  post,  so  as  to  be  steady  enough  to  give  an  easy  view  of  the  sun.  To  lessen  the  brilliancy  of  the  sun,  cover  the 
object-glass  witli  a  cap  having  a  round  hole,  three-fourths  of  an  inch  iu  diameter,  cut  in  its  centre.  The  spy-glass  will 
be  worse  than  useless  unless  one  is  accustomed  to  its  use,  and  has  it  fastened  so  as  to  be  steady.  A  smoked  glass  should 
also  be  prepared,  but  a  part  ol'  the.  glass  should  be  very  lightly  smoked. 

.tmoigrincnls  fur  iilm-i-ratimi. —  Each  observation  should  be  made  by  a  party  of  three  persons.  Only  one  instrument 
of  each  kind,  watch,  glass,  Ac.,  is  needed  by  a  party.  A  station  should  be  selected  where  they  win  be  free  from  all 
interruption,  either  in  the  open  air  or  at  an  open  window  facing  west.  One,  at  least,  of  the  party  must  have  a  pencil 
and  note-book  in  baud  to  record  the  time. 

The  obserratiou. — When  the  visible  part  of  the  sun  is  reduced  to  the  narrowest  crescent,  the  holder  of  the  watch, 
keeping  his  eye  on  the  face,  will  begin  to  count  the  seconds  aloud  ;*  the  holder  of  the  smoked  glass,  with  or  without  the 
spy-glass,  will  watch  for  the  hist  ray  of  true  sunlight,  being  careful  to  look  through  the  brightest  part  of  the  glass  the 
eye  will  bear  without  inconvenience  ;  and  the  third  observer,  if  there  be  one,  will  look  for  the  disappearance  of  sunlight 
with  the  naked  eye,  and  stand  ready  with  pencil  and  paper  to  record  the  time.  When  the  last  speck  of  the  sun  has 
disappeared,  the.  observer  with  the  glass  will  call  "time,"  and  the  exact  second  at  which  the  call  was  given  must  be 
immediately  written  down.  The  minute,  also,  must  be  carefully  noted  and  recorded. 

The  observers  will  then  await  the  return  of  sunlight,  the  count  of  the  seconds  being  kept  up,  if  the  face  of  the 
watch  can  be  seen,  which  it  probably  can  if  held  so  that  the  light  of  the  "corona"  shall  fall  upon  it.  The  duration  of 
total  eclipse  will  generally  fall  between  ball' a  minute  and  a  minute  and  a  half,  depending  on  the  position  of  the  observer. 
The  first  Hash  of  true  sunlight  will  seem  to  burst  out  suddenly,  and  the  minute  and  second  of  its  appearance  must  be 
recorded  with  the  same  care  as  the  lime  of  disappearance.  The  difference  of  the  two  times  gives  the  duration  of  totality. 

XlH-riiil  iireciiiiliiin*. — Iii  .judging  the  beginning  of  totality,  there  is  danger  of  error  from  two  sources.  The  first  is 
that  the  sun's  crescent  may  become  so  narrow  as  to  become  invisible  through  the  smoked  glass,  if  it  be  too  dark,  several 
seconds  before  it  is  really  all  covered,  and  thus  the  observer  may  call  "time"  too  soon.  Such  a  mistake  maybe  detected 
and  corrected  by  the  (bird  observer  looking  on  with  the  naked  eye,  if  the  following  circumstance  be  attended  to : 

Tin  lii'i/iiiniiiii  <>f  total  eclipse  in  marked  Iii/  a  i'<ry  rapid  increase  in  the  darkness,  caused  ly  the  advent  of  lite,  moon's  shadow. 
If,  then,  the  darkness  increases  more  rapidly  after  '-time"  is  called  than  it  did  before,  time  was  called  too  soon,  and  must 

be  repeated. 

The  other  danger  is  of  the  opposite  kind,  and  should  be  equally  avoided.  It  is  that  the  light  of  the  brilliant  rose- 
colored  protuberances  which  surround  the  dark  body  of  the  moon  during  the  total  eclipse  may  be  mistaken  for  sunlight, 
and  thus  the  critical  moment  be  suffered  to  pass.  In  this  case  each  observer  must  determine  separately  as  to  the  exact 
second  at  which  it  ceased  to  grow  darker,  and  if  they  agree  within  one  or  two  seconds,  the  time  thus  judged  may  be 
supposed  correct,  and  each  one's  estimate  may  be  written  down  separately. 

The  observer  with  the  smoked  glass  will  be  most  liable  to  the  first  of  these  mistakes  ;  the  naked-eye  observer  to 
the  last. 

The  return  of  sunlight  will  also  be  preceded  by  a  reddish  glow  on  the  border  of  the  dark  moon,  which  must  not  be 
mistaken  for  the  sun.  Indeed,  if  the  observers  be  near  the  edge  of  the  shadow,  it  is  probable  that  this  red  glow,  which 
comes  from  the  hydrogen  atmosphere  of  the  sun,  may  bo  visible  during  the  whole  time  of  totality. 

All  the  recorded  times,  with  an  estimate  of  the  uncertainties  to  which  the  observers  think  they  were  liable,  and  a 
statement  of  the  place  where  made,  giving  distance  in  miles  and  direction  from  the  court-house,  if  it  be  a  county  town, 
and  from  the  railroad  station,  if  a  railroad  pass  through,  should  be  immediately  certified  by  the  signatures  of  all  three 
observers,  and  forwarded  to  the  Naval  Observatory,  Washington. 

It  is  particularly  requested  that  each  party  send  oft"  its  report  before  comparing  notes  with  any  other  party  ;  also, 
that  the  original  pencil  record,  however  imperfect,  accompany  the  report.  All  will  be  carefully  preserved  in  the 
archives  of  the  observatory  for  the  use  of  astronomers. 

Statements  of  which  the  following  are  abstracts  were  received  in  reply  to  the  circular.    In 

*  It  would  be  well  for  the  observers  of  each  party  to  practice  beforehand  the  counting,  calling,  and  recording. 


16 


REPORT    OF   PROFESSOR   NEWCOMB. 


explanation  of  these  it  is  to  be  remarked  that  many  of  the  positions  are  referred  to  the  public  land 
surveys,  which  afford  the  means  of  determining  the  geodetic  difference  of  longitude  between  any 
two  points  nearly  east  and  west  of  each  other,  and  the  difference  of  latitude  between  points  north 
and  south  of  each  other,  with  considerable  precision. 

The  longitudes  and  latitudes  of  some  points  in  Iowa  have  been  determined  from  Colton's  large 
sectional  map  of  that  State.  The  positions  of  Des  Moines,  Hock  Island,  and  other  stat  ions,  are  as 
follows : 


Position  011  map. 

Known  positions. 

Corrections. 

£,,                  .     . 

# 

% 

0 

A 

t 

A 

o      / 

O         ' 

t 

, 

DesMoiiies,  (C.  H.)  . 

41  35.0 

16  40.3 

41  35.0 

1C  34.  2 

0.0 

-    6.1 

Rock  Island    .     .     . 

41  29.8 

is  37.  9 

41  30.6 

16  31.  H 

+    0.  H 

-    6.1 

Marion  

42     1.  5 

14  39.6 

Mechanicsville     .     . 

41  53.0 

14  12.8 

Red  Oak     .... 

41  ,11.0 

14  12.8 

The  adopted  positions  of  the  last  three  places  are  found  by  applying  the  systematic  corrections 
thus  deduced. 

In  Illinois  the  same  method  could  not  be  applied  owing  to  the  enormous  errors  with  which  the 
degrees  of  longitude  are  affected  on  Colton's  map.  The  positions  of  a  few  points  near  Rock  Island 
are,  however,  fixed  by  measurement  along  the  lines  of  the  public  surveys  as  laid  down  on  the  map. 
The  adopted  position  of  llock  Island  is  from  Colonel  Graham's  report  of  1859. 

When  the  letters  S.  H.  follow  the  names  of  the  observers,  it  indicates  that  they  seem  to  be 
signed  in  the  same  handwriting. 

The  word  "Original"  signifies  that  the  original  pencil  record  of  the  observations  was  forwarded, 
and  that  the  limes  given  are  an  exact  transcript  therefrom. 

I. — OBSERVATIONS   NEAR   THE   NORTHERN  LIMIT. 

MARION,  IOWA.— Latitude  42°  2'.1;  longitude  11°  33'.5. 

First  station. — Court-house  cupola,  22i  chains  south,  and  2i  chains  east  of  the  comers  of  town- 
ships 83  and  84,  range  0  and  7  west,  5  p.  m. 

Observers. — G.  A.  Gray,  county  surveyor;  J.  W.  McClellan,  ,T.  G.  Hayzlett. 
Instrument. — Engineer's  transit,  ap.  1 J  inch ;  power  20. 


Beginning  of  eclipse 
Beginning  of  totality 
End  of  totality 
End  of  eclipse 
Duration  of  totality 
Error  of  watch  not  given,  and  probably  unknown. 


) 


m.       s. 

3  4G     50 

4  48    15 

4  49     18  ^  Original. 

5  45       7 

1       3 

Observations  of  meteoric  appearances,  and 

of  contact  with  spots,  accompany  the  report.     Observers  express  confidence  in  the  precision  of  their 
observations. 

Second  xtiition.— One-sixteenth  mile  north  of  court-house,  and  one-fourth  mile  north  of  depot. 
Observers.— E.  M.  Smith,  M.  D.,  Samuel  W.  Durham,  J.  W.  McElhenny. 

h.      m.       n. 

Total  phase  "  on,"  (naked  eye)  4    53      4  ~) 

Total  phase  "  on,"  called  4    53      5  >  Original. 

Total  phase  "  off "  -  4    54    19) 

Obseivers  think  the  time  called  was  one  second  "  slow,"  and  so  give  the  duration  lm  l.V. 
Third  station.— Near  northwest  corner  of  township  83,  range  6  west.  5  p.  m. 
Observers. — E.  L.  Samson,  James  B.  Graves,  George  W.  Holmes. 
Instruments. — Field-glass,  smoked  glass,  four-second  watch. 


OBSERVATIONS    OF    THE    ECLIPSE    OF   AUGUST   7,    1809. 


17 


Ml. 

55 

57 
1 


52 
11 
19 


Original,  but  the  last  sec- 
onds  are  changed  from 
15  to  11. 


Commencement  of  total  eclipse    -  4 

End  of  total  eclipse  4 

Duration  of  totality 
>l  We  think  our  observations  are  very  nearly  correct." 
MEOHANTCSVILLE,  IOWA. — Latitude  41°  53'.6 ;  longitude  14°  6'.7. 
Station.— Eighty-five  rods  northwest  from  Chicago  and  Northwestern  railroad  depot. 
Observer*. — Homer  S.  Bradshaw,  John  F.  Golding,  P.  E.  Bradshaw.     S.  H. 


Original. 


Time  called  by  both  observers 
Time  called  by  naked-eye  observer 
Duration  of  totality 
KED  OAK,  IOWA.— Latitude  41°  51'.5 ;  longitude  14°  6'.7. 

Station. — Section  1,  township  81  north,  range  3  west  of  5th  P.  M.,  two  miles  due  south  of  Stan- 
wood,  O7i  Chicago  and  Northwestern  railroad. 

Observers. — Samuel  Yule,  (with  spy-glass,)  E.  B.  Cousins,  (naked  eye,)  G.  F.  McClelland,  (smoked 
glass,)  M.  L.  Simmons,  (watch.) 

7i. 

Beginning  of  totality,  spy-glass  4 

Beginning  of  totality,  naked  eye  4 

Beginning  of  totality,  smoked  glass     -  4 

End  of  totality,  spy-glass  4 

End  of  totality,  naked  eye  4 

End  of  totality,  smoked  glass  4 

Duration  of  totality 
BOCK  ISLAND,  ILL — Latitude  41°  31'.5 ;  longitude  13°  31'.5. 
First  station. — Near  United  States  arsenal,  on  the  west  end  of  Eock  Island. 
Observations  made  by  two  parties  are  communicated  by  Brevet  Brigadier  General  T.  J.  Bod- 
man,  United  States  Army. 

0&se>TtT.v.— Captain  and  Brevet  Major  F.  H.  Parker,  Captain  Clifton  Comly,  Lieutenant  Henry 
Metcalf,  all  of  the  Ordnance  Department,  United  States  Army. 
Instruments. — Watch  and  smoked  glasses. 


in. 
50 

no 

50 
51 
51 
51 
1 


44 
43 
42 

48 
47 
46 
4  3 


Original. 


in. 

58 
0 
1 

57 
1 


48 
3 


20 
33 
17 


•  Original. 


First  contact  3 

All  obscure  5 

First  light  5 

Last  contact  -  5 

Duration  of  total  phase 
Watch  9s  fast. 

Three  other  times  of  last  contact  were  recorded,  beginning  at  51'  55™  40s,  which  the  observers 
attributed  to  the  fatigue  of  their  eyes.    They  agree  that  the  latest  recorded  time  was  the  true  one. 
Observers. — Captain  Morris  Schaff,  Brevet  Captain  M.  S.  Poland,  and  Lieutenant  W.  P.  Butler, 
Ordnance  Department,  United  States  Army. 
Instruments. — Not  stated. 


By  telescope. 

By  the  eye. 

/I.       Ml.          H. 

A.      TO.        S. 

Meau  solar  local  time  of  beginning  of  eclipse  . 

3    58    29 

3    58    29 

Mean  solar  local  time  of  beginning  of  totality 

4     59     47 

4     59    44 

Meau  solar  local  time  of  ending  of  totality 

514 

5       1       4 

Mean  solar  local  time  of  ending  of  eclipse   .     .     . 

5    57      7     '       5     57       7 

Duration  of  totality  

1     17 

1     20 

3« 


18  REPORT   OF   PROFESSOR   NEWCOMB. 

Second  station. — Near  court-house,  on  fractional  quarter  section  35  of  township  18  north  of  base- 
Hue,  and  range  2  west  of  4th  P.  M. 

Observers. — Marcus  B.  Osborn,  John  E.  Humes,  John  F.  Corker. 

(The  results  of  the  observations  are  withheld  for  explanations  from  the  observers.) 

COLONA,  ILL.— Latitude  41°  29'.S;  longitude  13°  IX'.O. 

Station. — House  of  Mr.  Bell,  one-third  mile  northwest  of  the  13th  mile-post  east  from  Rock 
Island,  on  the  Chicago,  Rock  Island  and  Pacific  railroad,  and  at  the  northwest  corner  of  northeast 
quarter  of  section  11,  township  17  north,  range  1  east. 

Observers. — Mr.  and  Mrs.  James  Bell,  Rev.  and  Mrs.  S.  H.  \Veed. 

Instruments. — Elgin  watch,  and  smoked  glass. 

Duration  of  total  phase,  0'"  59s  (17m  35s  — 1G">  30s.) 

Original  record  not  sent,  but  the  description  of  the  observations  and  phenomena  is  sufficiently 
minute,  precise,  and  satisfactory  to  inspire  confidence  in  the  observations. 

GENESEO,  ILL. — Latitude  41°  27'.4 ;  longitude  13°  G'.4. 

First  station.* — One  hundred  feet  south  of  passenger  depot  of  Chicago,  Rock  Island  and  Pacific 
railroad. 

Observers. — L.  C.  Campbell,  notary  public;  J.  F.  Dresser,  banker;  John  Reiter,  dentist;  C.  E. 
Parker,  merchant;  F.  Stein,  jeweler. 

ll.      II).         S. 

First  appearance   -  4    6    00    "J 

Commencement  of  totality  5    8    23 


Close  of  totality  5    8    56J 

Disappeared  (5     5    30 

.Duration  of  totality  0    33J 


Original. 


Second  station. — About  four  miles  south  of  Geneseo;  or,  accurately,  the  northwest  corner  of 
section  8,  township  1C  north,  range  3  east  of  4th  P.  M.     Latitude  41°  24'.i;  longitude  13°  S'.O. 
Observers. — E.  C.  Moderwell,  W.  C.  Brown,  M.  1).,  John  Smith. 

Duration  of  totality,  5SS  ±  2s  (2'»  29s—)  1"'  31s. 
Original  record  not  forwarded. 

LACON,  ILL. — Doctor  and  Mrs.  George  Davis  give  a  duration  of  2  minutes  0  seconds,  but  are 
iiot  certain  of  its  correctness.     It  must  be  incorrect,  as  Lacon  is  very  nearly  on  the  limit. 

CHKNOA,  ILL. — Station. — Near  southeast  corner  of  section  2,  township  2fi,  range  4. 
Observers. — C.  S.  Elder,  M.  D.     (The  others  have  not  signed.) 
Duration  of  totality,  .">9.J-S  —  lls  =  48is.  •(Original.) 

EL  PA.SO,  ILL. — Station. — 1,!»S5  feet  east  and  41G  feet  north  from  railroad  station. 

Observers. — Joseph  11.  Moore,  W.  R.  Torrey,  G.  L.  Gibson. 

Instruments. — Watch,  smoked  glass,  and  achromatic  telescope  lashed  firmly  to  a  round  post. 

/).        Ml.  8. 

Beginning  of  eclipse  4     10    30  ^j 

Beginning  of  totality     -  -      •  -  5    10    30  [ 

Knd  of  totality  5     12    28  fChlcaS°  *''»'• 

End  of  eclipse  0       9    30  J 

Original  record  not  forwarded. 

GRIDLEY,  ILL. — Station. — One-half  mile  north  of  station-house,  and  in  the  center  of  section  4, 
township  2G  north,  range  3  east  of  3d  P.  M. 

Observers. — Two  parties  of  three  in  each.     Observations  communicated  by  W.  II.  Boris,  who 
says  the  two  parties  agreed  perfectly,  so  they  deem  it  unnecessary  to  send  separate  reports. 
Duration  of  totality,  5h  I"1  5s  — 5h  =  l™  5s. 
Original  record  not  forwarded. 

*  The  next  party  refer  to  this  station,  and  give  its  position  as  near  center  of  section  21,  township  17  north,  range  3 
east  of  4th  P.  M.    The  longitude  and  latitude  have  been  deduced  from  this  statement. 


OBSERVATIONS    OF   THE    ECLIPSE    OF    AUGUST    7,    1869.  19 

PAXTON,  ILL.  —  First  station.  —  One  thousand  feet  south  15°  east  from  court-house. 

Observers.  —  II.  J.  Howe  and  W.  H.  Pells,  observers  ;  E.  T.  Glasener,  time-counter  ;  John  M. 
Ilanley  and  Lewis  K.  Jones,  tally-keepers. 

Duration  of  totality,  20'»  30s  —  20™  2s  =  28s.     (Original.) 

Second  station.  —  Three-fourths  mile  southeast  of  court-house. 

Obsen-ers.—  Professor  T.  N.  Hasselquist,  A.  E.  Corwin,  Rev.  J.  S.  Harkey,  -  —  ,  stu- 

dent. (S.  H.) 


DANVILLE,  ILL.  —  First  station.  —  Three-fourths  mile  southeast  of  court-house. 
Observers.—  Warren  Dunbar,  (eye,)  J.  G.  English,  (time,)  J.  C.  Winslow,  (glass.) 

/I.         HI.  8. 

Time  of  beginning  --       4    14    15  J 

Time  of  beginning  of  totality  5     13      0 

Time  of  end  of  totality  -  5     14      6 

Time  of  eud  of  eel  i]  isc  6      5    20  }•  Apparently  original. 

Naked  eye  — 

Time  of  beginning  5     12     54 

Time  of  ending  5     14       6  3 

All  these  agree  that  the  naked  eye  observer  called  "time"  too  soon,  so  that  the  duration  of 
totality  was  I1"  (is.  t 

Second  station.  —  Near  center  of  section  8,  township  19  north,  range  11  west  of  2d  P.  M. 
Observers.  —  VV.  T.  Cunningham,  Win.  P.  Chandler,  Theo.  Lemon. 

h.      m.        8. 

Eclipse  commenced  4    15    30  ) 

Time  called  for  5     16     10  !  Q 

Time  called  for  second  time  •  5     17     21  | 

Duration  of  total  phase  1     11  J 

COLUMBUS,  IND.  —  First  station.  —  Two  and  three-fourths  miles  west  of  Columbus. 
Observers.—  Rev.  N.  S.  Dickey,  L.  VV.  Comstock,  Albert  T.  Beck. 
Duration  of  totality,  lm  4s.     (No  original  record.) 
Second  station.  —  Not  given. 
Observer.  —  Doctor  (leo.  <i.  Rabb. 
Duration  of  totality,  I"1  .'!0S.     (No  original  record.) 
Third  station.  —  One  mile  north  of  court-house. 
Observer.  —  Professor  A.  H.  Graham. 
Duration  of  totality,  lm  19s.     (No  original  record.) 
FRANKLIN,  IND.  —  Station.  —  Near  court-house. 
Observers.—  Ke\  '.  J.  B.  Morey,  Professor  F.  W.  Brown,  Professor  J.  S.  Houghain,  W.  T.  Stott. 

h.  in.  s. 

Beginning  5  25  58    First  call  29  too  soon. 

5  26      0    True  call. 

Kuding  ~>  26  37 

EDINBURG,  INU.  —  station.  —  Three  hundred  yards  north  of  railroad  station. 
Observer.  —  Rev.  John  B.  Logan,  without'assistance. 
Instruments.  —  Watch  and  smoked  glass. 

/I.         HI.  «. 

First  appearance  on  northwest  part  of  sun  -  4  10 

Total  darkness,  lasting  40  seconds  5  12          !  Qri   iual  recol.d. 

Sun  began  to  appear  ;  streaks  still  appear  ; 

darker  than  bright  moonlight   -  5  12    40  J 


20  REPORT    OF   PROFESSOR   NEWCOMB. 

MOUNT  VERNON,  IND. — Slation. — Masonic  Hall.  From  the  section  lines  it  is  deduced  that  the 
station  is  1.074  statute  mile  east,  aud  13.8  statute  miles  south,  of  a  point  of  New  Harmony,  the  posi- 
tion of  which  was  determined  by  the  Coast  Survey  in  1848,  as  follows:  latitude,  38°  7'  50";  longi- 
tude, 5"  51«>  20s. 

Observers. — Aaron  Baker,  C.  E.,  S.  H.  Pearse,  M.  D.,  S.  Milner. 

Instrument. — Engineer's  transit — aperture,  :f  in.;  power,  10. 

It.      m.        *. 

Beginning  of  eclipse  4  25  27  } 

Beginning  of  total  phase  5  24  7!l  I 

Ending  of  total  phase   -  5  20  55  (  ( 

Ending  of  eclipse  0  21  58  I 

Duration  of  totality  1  30 
CARLISLE,  KY. — Station. — Not  given. 
Observers.— E.  C.  H.  Willoughby,  Dr.  W.  W.  Fritts,  Charles  Boynton. 


37  i 
20  J 


'  Original. 


Totality  lasted  1    43 

At  the  beginning  of  obscuration  one  observer  called  "  time  "  two  seconds  earlier  than  the  other. 
The  last  call  was  adopted. 

FRANKLINTON,  K.  C. — Station. — One  hundred  and  sixty  yards  west  of  railroad  depot. 

Observers. — George  W.  Neal,  A.  M.,  C.  W.  Conway,  Calvin  Pritchard,  Robert  N".  Winston. 

Instruments. — Spy-glass,  smoked  glass,  and  racer's  watch,  with  long  second  hand. 
Total  eclipse  lasted  03  seconds,  per  spy-glass  observer. 
Total  eclipse  lasted  01  seconds,  per  naked-eye  observer. 

(No  original  record.) 

WILSON,  WILSON  COUNTY,  N.  C. — Station. — Not  given. 

Observers. — Jno.  W.  Dunham,  Jno.  McBride,  Robert  S.  Husk,  J.  A.  Fugua,  Eev.  A.  A.  Bentou. 

Instruments. — Camera  obscura  and  smoked  glass. 

The  original  record  is  sent,  by  which  it  appears  that  the  three  first  observers  agreed  upon 
G1'  0™  27s  as  the  time  of  beginning  of  total  phase,  and  the  two  first  each  observed  O1'  I111  51s  as  that 
of  ending;  but,  in  the  record,  the  commencements  by  D.  and  H.  seem  to  be  altered  to  agree  with 
McB.  H.  "noticed  the  obscuration  as  total  in  the-glass,  and  removed  it  before  calling;"  but  no 
reason  is  given  for  the  change  of  D.'s  observations  from  22s  to  27s. 

II. — STATIONS   NEAR   THE  SOUTHERN   LIMIT. 

HANNIBAL,  Mu. — First  station. — House  of  Eev.  Jno.  Leighton. 

Observers. — Eev.  Juo.  Leighton,  G.  H.  Shields,  W.  B.  Fiero.    The  latter  does  not  sign  the  report. 

Instrument. — Thirty-inch  spy-glass. 

/I.         HI.  *. 

Commenced,  (observer  with  glass)  5      1    10  ") 

Commenced,  (observer  with  naked  eye) '  5      1    10  I          . 

Ended,  (observer  with  glass)  5      3    10   i 

Ended,  (observer  with  naked  eye)  5      3      8  J 

The  seconds  of  ending  both  seem  to  have  been  corrected  or  twice  recorded. 
Second  station. — 1,208  feet  north  29°  west  from  railroad  depot. 
Observers.— H.  M.  Sutnner,  C.  E.,  F.  B.  Lockliug,  C.  E.,  E.  L.  Corthell,  C.  E.,  G.  H.  Williams. 

ll.        III.          S. 

Total  phase  begins,  (through  glass)  5      8    52  "| 

Total  phase  ends,  (through  glass)  -  5    10    49  I  „  _.  f.     . 

Total  phase  begins,  (naked  eye)  5    10    49  f 

Total  phase  ends,  (naked  eye)  5    10    49  J 

The  observers  give  the  first  observation,  5''  8m  523,  as  the  true  time  of  beginning.  The  third  is 
probably  2'"  wrong,  through  inadvertence  in  recording. 


OBSERVATIONS    OF    THE    ECLIPSE    OF   AUGUST    7,    1869.  21 

BOWLING  GREEN,  Mo. — Fii-xt  station. — Court-house 

Observers.— 3.  W.  Basyc,  Melville  Smith,  Albeit  Cluster,  Mrs.  L.  E.  Basyp.     (S.  H.) 

/I.        111.          8. 

Total  eclipse  begins  4    51     41  | 

Continued  51  j 

In  the  accompaaying  report  the  end  is  given  at  41'  40™  32s,  and  a  duration  of  51  seconds  thence 
deduced. 

Second  station. — Residence  of  Augustus  C.  Sheldon,  50  rods  south  of  court-house. 

Observers. — Augustus  C.  Sheldon,  Nellie  H.  Sheldon,  W.  P.  Lawry. 

The  observers  sign  a  certificate  that  they  made  particular  observation  of  the  duration  of  the 
total  eclipse,  and  found  it  to  be  forty-six  (40)  seconds.  No  original  record  forwarded. 

ALTON,' ILL. — Station. — Near  quarter-section  corner  on  the  line  between  sections  33  and  34, 

township  (i  north,  of  range  10  west  of  3d  P.  M. 
Observers. — T.  M.  Long,  county  surveyor. 
Instrument. — Transit  compass,  with  telescope  attached. 

h.      )/i. 

Beginning  of  eclipse  4  1,3 

Total  obscuration  5  11 

Return  of  light  5  llf 

Ending  of  eclipse  0  7i 
~No  original  record  forwarded. 

CARLYLK,  ILL. — Station. — 1,100  feet  south  of  west  of  court-house,  and  1,100  feet  north  of  west 
of  the  depot,  on  the  Ohio  and  Mississippi  railroad. 

Observers.— Zophar  Case,  .lames  Harkley,  William  A.  Robinson. 

h.  m.  s. 

Commencement  of  obscured  light  of  sun  4  15  3 

Total  obscuration  5  15  39 

First  sunlight  517  6 

Disappearance  of  any  obscuration  of  sun  0  11  50 

Duration  of  totality  1  '21 
No  original  record,  but  the  report  is  duly  certified. 

HENDERSON,  KY. — /Station. — P>ank  of  Ohio  River,  four  squares  from  court-house. 
Observers.— T.  H.  Crosby,  C.  E.,  P..L.  Blacknell,  president  Ghent  College.    (S.  H.) 
Instrument. — Engineer's  transit,  with  telescope  of  1^  inch  aperture  and  13  inches  long. 

h.      m.        ». 

Beginning  of  total  eclipse  5    22    30  i 

End  of  total  eclipse  5    24      0  I  OnSlual- 

OAKLAND  STATION,  KY.— First  station.— Oakland  Station,  on  the  Louisville  and  Nashville  rail- 
road, 11.3  miles  north  00°  east  from  Bowling  Green. 

Observers.— John  E.  Young-love,  Jno.  J.  Ililburn,  Lieutenant  W.  1.  Reise,  C.  R.  Edwards. 

Beginning  of  total  phase,  (to.  s.  t.  of  Bowling       /,.    ,„.     8. 
Green)  5    24    30 

End  of  total  phase  5    24    33 

Duration,  three  seconds. 
No  original  record  sent. 

"The  beginning  of  total  phase  was  very  accurately  taken,  both  observers  giving  the  same 
instant,  but  we  deem  it  proper  to  acknowledge  our  doubt  as  to  the  exact  time  of  ending.    We  had 
expected  a  total  phase  of  some  20  or  30  seconds,  and  were  so  much  surprised  at  the  sudden  reap 
pearance  of  the  sun  that  we  may  have  allowed  the  critical  moment  to  pass  unobserved." 


22 


REPORT   OF    PROFESSOR   NEWCOMB. 


Second  station. — One-fourth  mile  southwest  of  Oakland  Station,  11  miles  from  Bowling  Green. 
Observers. — J.  A.  Timmons,  A.  M.;  J.  L.  Donaldson,  A.  B.;  J.  M.  Youn glove,  A.  B. 
Instruments. — Smoked  glass  and  opera  glass. 


Beginning  of  totality 

End  of  totality 

End  of  eclipse 

Duration  of  total  phase,  about 


7l.  Ml.  S. 

.>  23  45 ") 

5  23  47 

fi  18  28 

0  0  2  j 


>  Original. 


"With  the  naked  eye  totality  was  iiot  plainly  visible;  the  corona  appeared  to  be  not  quite 
perfect,  and  many  mistook  the  reflection  from  the  sun  to  be  the  sun  itself,  thereby  causing  the 
belief  of  non-totality. 

"  The  stars  were  plainly  visible  with  jthe  naked  eye." 

The  watch  was  compared  with  a  meridian  mark  at  Bowling  Green. 


On  the  7th  it  stood 
Ou  the  8th  it  stood 


/i.      m.        8. 

12     5     28 
12     5     19 


BURKSVILLE,  KY. — First  station. — Not  given. 

Observers.— V*.  G.  Hunter,  M.  D.;  J.  W.  Williams,  clerk  circuit  court ;  L.  A.  WaggeuerJ  clerk 
county  court;  Scott  Walker,  attorney  at  law. 

Duration  of  total  eclipse,  1"'  16s. 

The  original  record  is  forwarded,  but  is  not  clear.  The  duration  seems  to  have  been  counted 
from  the  moment  of  obscuration,  independently  of  the  absolute  time. 

Second  station. — Not  given. 

Observers. — B.  M.  Alexander,  with  two  others  who  do  not  sign  the  report. 

Total  eclipse  began  37  minutes  past  5,  and  lasted  1 "'  2SS,  which  is  considered  only  approxi- 
mately true. 

III. — DURATIONS  OBSERVED  AT  POINTS  TOO  FAR  WITHIN  THE  SHADOW  TO  BE  t'SED  IN  FIXING  ITS 

LIMITS. 

These  observations  being  valuable  principally  as  atlbrding  data  for  judging  of  the  general 
Accuracy  of  extemporized  observers,  it  is  deemed  unnecessary  to  give  more  than  I  he  observed  dura- 
tion and  the  name  of  thp  person  by  whom  it  is  communicated. 


Place. 

Lat. 

Long. 

Duration. 

• 
Communicated  by  — 

Remarks, 

o 

m.    «. 

Midway,  Ky  -     -     -     - 

. 

7 

2  24 

Ensign  David  N.  Bell,  U.  S.  N  . 

One  mile  north  of  railroad  sta- 

Tayloraville, N.  C    .     . 

. 

4 

2    15 

A.  C.  bo.vd  <•!  nl. 

tion. 

3 

•i     17 

J.  A.  McDonald  i'l  nl. 

Davidson  College    .     . 

. 

3 

2      8 

Professor!'.  Phillips    - 

Two  other   observations  gave 

River  View   . 

. 

3 

2    20 

M.  I!ald\vin  1  1  nl. 

2™  fl8  and  2m  10B,  of  which  the 

:', 

2    25 

.John  A.  Raiiisrv. 

lirst  is  doubtful. 

3 

2    35 

\V.  11.  1,'obbins. 

3 

2    13 

F.  C.  Robbins. 

Chanel  Hill   .... 

1 

2       5 

James  J!.  Mason  (/  ul. 

Kalcigh    

-      - 

1 

1     58 

'William  Primrose  <•/  ill.      .     . 

Mean  of  two  observations. 

REPORT 


PROCESSOR  WILLIAM  HAROESS,  U.  S 


REPORT   OF    PROFESSOR    WILLIAM    BARENESS,  U.  S.  N. 


UNITED  STATES  NAVAL  OBSERVATORY, 

Washington,  October  1,  18G9. 

SIR  :  I  have  the  honor  to  submit  the  following  report  in  relation  to  the  astronomical  and  spec- 
troscopic  observations  made  by  me  in  connection  with  the  expedition  sent  out  to  Iowa,  by  this 
Observatory,  for  the  purpose  of  observing  the  total  solar  eclipse  of  the  7th  of  August  last. 

INTRODUCTORY. 

Onr  instruments  and  apparatus  were  delivered  to  Adams  Express  Company  on  Saturday,  July 
;?,  to  be  forwarded  to  Des  Moines,  in  the  State  of  Iowa ;  and  the  party  left  Washington  on  the  even- 
ing of  the  following  Monday.  At  that  time,  owing  to  the  absence,  of  any  exact  determination  of 
the  positions  of  the  towns  and  villages  near  t  he  ecu  I  nil  line  of  the  eclipse,  we  had  not  decided  defi- 
nitely what  station  we  would  occupy,  but  it  seemed  probable  that  the  most  favorable  point  would  be 
Mitchellville,  a  small  village,  situated  on  the  Chicago,  Rock  Island  and  Pacific  railroad,  whose  bear- 
ing from  Des  Moines  is  north  05°  east,  and  its  distance  13.2  miles.  About  noon  on  Saturday,  July 
10,  we  reached  Des  Moines,  and  upon  going  to  the,  hotel  I  met  Mr.  E.  P.  Austin,  of  the  Unite*? 
States  Coast  Survey,  who  was  engaged  in  obtaining  the  geographical  position  of  the  city.  His 
observations  were  not  then  finished,  but  they  showed  that  it  was  not  more  than  eleven  or  twelve 
miles  to  the  southwest  of  the  central  line  of  the  eclipse.  The  duration  of  the  totality  there  would, 
therefore,  be  less  than  two  seconds  shorter  than  on  the  central  line  itself,  and  as  a  city  of  sixteen 
thousand  inhabitants  necessarily  offered  many  facilities  which  we  could  not  expect  in  a  small  vil- 
lage, we  at  once  decided  to  remain  in  Des  Moines. 

SITE  OF  TEMPORARY  OBSERVATORY. 

Saturday  afternoon  and  the  following  Monday  were  spent  in  selecting  a  site  for  our  observa- 
tory, and  as  we  were  to  the  southwest  of  the  central  line  of  the  eclipse  we  confined  our  reconnais- 
sance to  the  northeastern  part  of  the  city.  The  spot  which  seemed,  in  all  respects,  the  most  desir- 
able is  situated  on  the  northwest  corner  of  Second  and  Short  streets.  It  is  a  high  piece  of  vacant 
ground  on  the  west  bank  of  the  Des  Moines  River,  with  a  horizon  almost  entirely  devoid  of  obstruc- 
tions, and,  as  the  city  is  not  built  up  so  far  north,  there  is  no  travel,  and  it  is  perfectly  free  from 
that  great  enemy  of  photography,  dust.  There  is  also  a  well  of  water  near,  which  we  thought  A 
decided  advantage,  but  upon  trial,  afterwards,  it  proved  to  be  useless  for  photographic  purposes. 
I  ascertained  that  this  land  belonged  to  Mrs.  Sytha  .1.  Hall,  and  thai  her  agent  in  the  city  was  Mr. 
J.  M.  Ballinger.  On  Tuesday  morning  I  called  upon  him  and,  after  stating  the  case  to  him,  he  said 
that  he  was  sure  Mrs.  Hall  would  be  very  glad  to  have  us  place  our  observatory  there,  and  we  had 
his  permission  to  do  so.  No  charge  was  made  for  the  use  of  the  land,  and  our  thanks  are  due  to 
him  and  Mrs.  Hall  for  their  kindness  in  the  matter. 

THE  TEMPORARY  OBSERVATORY. 

On  the  afternoon  of  July  13  I  called  upon  Mr.  F.  T.  Nelson,  a  builder  whom  I  can  confidently 
recommend,  and  made  arrangements  with  him  to  erect  our  temporary  observatory.  He  set  some 
of  his  men  to  work  at  it  next  morning,  intending  to  have  it  finished  in  two  or  three  days,  but  before 
noon  the  weather  changed  and  a  series  of  thunder-storms  set  in  which  lasted,  -with  short  intermix 

4* 


26  REPORT    OF    PROFESSOR    ITARKNESS. 

sions,  lor  the  next  five  days.  The  men  managed  to  do  some  work  between  the  storms,  but  their 
progress  \v;is  necessarily  slow,  and  it  was  the  afternoon  of  July  20  before  the  building  was  finished. 
As  soon  as  the  carpenters  were  done  we  sent  to  the  express  office  for  our  instruments  and  appa- 
ratus, and  by  six  o'clock  that  evening  the  boxes  containing  them  were  all  safely  stored  in  the 
observatory. 

Plate  I  is  a  general  view  of  the  building  from  a  photograph  by  Mr.  E.  J.  Ward,  and  Plate  II 
is  a  plan  of  it  drawn  to  a  scale  of  one-quarter  of  an  inch  to  a  foot.  It  was  thirty-two  feet  long  by 
sixteen  feet  wide,  constructed  of  rough  pine  boards,  and  so  placed  that  Ihe  ridge  of  its  roof  ran 
almost  exactly  north  and  south ;  the  longest  sides  of  the  building  facing  respectively  to  the  east 
and  west.  The  eaves  of  the  roof  were  8.5  feet  above  the  ground,  and  the  boarding  on  the  sides  of 
the  building  was  horizontal,  that  on  the  east  side  being  continued  quite  up  to  the  roof,  while  that 
on  the  west  side  was  only  carried  to  the  height  of  five  feet  above  the  ground,  except  for  a  space  of 
seven  feet  at  the  north  end  of  the  building,  where  it  was  carried  quite  up  to  the  roof.  This  space, 
seven  feet  in  length  and  sixteen  feet  in  width,  was  partitioned  off  and  inclosed  as  a  dark  room  for 
photographic  purposes.  A  complete  description  of  it,  and  all  its  arrangements,  will  be  found  in 
Dr.  Curtis's  report.  The  seven  and  three-quarter  inch  telescope  was  mounted  exactly  in  the  cen- 
tral line  of  the  building,  that  is,  eight  feet  from  either  side,  and,  in  order  to  permit  its  use  from 
the  western  horizon  quite  up  to  the  zenith,  the  ridge  of  the  roof,  which  was  sixteen  feet  above  the 
ground,  was  placed  two  feet  to  the  east  of  the  central  line.  All  the  space  on  the  east  side  of  the 
ridge  pole,  and  eight  feet  of  the  north  end  of  that  on  the  west  side,  (sufficient  to  cover  the  photo- 
graphic dark  room,)  was  roofed  over  with  boards.  The  remaining  space,  twenty  five  feet  in  length, 
on  the  west  side  of  the  ridge  pole,  was  covered  with  canvas  (furnished  by  the  United  States  Arm\ 
Medical  Museum)  which,  at  the  cave,  passed  over  a  movable  horizontal  rail,  and  thence  down  to 
the  board  side  of  the  building,  which,  as  before  stated,  was  here  only  five  feet  high.  When  the 
telescopes  were  in  use  this  canvas  roof  was  rolled  up  like  an  awning,  and  the  horizontal  rail  was 
removed,  thus  affording  a  perfectly  unobstructed  view  of  all  that  portion  of  the  heavens  traversed 
by  the  sun  between  noon  and  sunset.  The  north  and  south  ends  of  the  building  were  covered  with 
boards  placed  vertically,  and  the  door  for  entrance  was  situated  in  the  south  end.  Suitable  open- 
ings for  ventilation  were  placed  in  the  gables  near  the  roof.  With  the  exception  of  those  in  t  lie- 
dark  room,  there  were  no  windows,  the  light  coming  in  through  the  canvas  roof  being  sufficient  for 
all  purposes. 

The  ground  upon  which  the  observatory  stood  is  clay,  and  as  it  is  well  known  that  clay  sprin- 
kled with  powdered  lime  soon  produces  a  very  hard  surface,  I  thought  that  a  sufficiently  durable 
floor  might  be  obtained  in  that  way.  Upon  trial,  however,  it  was  found  that  the  constant  walking 
on  it  gave  rise  to  such  a  quantity  of  dust  as  would  have  rendered  it  utterly  impossible  to  take  good 
photographs,  and  J  was  obliged  to  have  a  floor  of  planed  boards  put  down.  Owing  to  the  irregu- 
larity of  the^round  the  southern  part  of  this  floor  was  laid  five  and  one-quarter  inches  higher  than 
the  northern,  thus  making  a  step  between  the  two,  as  shown  on  the  plan. 

By  Thursday,  July  22,  the  large  telescope  was  mounted,  and  on  the  following  day  a  photograph 
of  the  sun  was  made,  and  some  observations  for  time  and  latitude  were  taken.  The  equatorial 
adjustments  of  the  large  telescope  were  completed  on  July  24,  and  from  that  time  till  August !)  pho- 
tographs were  taken  and  observations  made  every  day  when  the  weather  pennitted. 

THE  INSTEUMENTS  EMPLOYED. 

An  Achromatic  Telescope  of  seven  and  three-quarters  inches  clear  aperture,  equatorially  mounted 
and  provided  with  a  driving  clock  and  divided  circles,  belonging  to  the  United  States  Naval  Acad- 
emy, was  kindly  lent  to  the  observatory  by  Vice- Admiral  I).  I).  Porter,  to  be  used  for  photograph- 
ing the  eclipse.  The  necessary  alterations  to  fit  it  for  that  purpose  were  made  under  my  supervision, 
and  much  credit  is  due  to  Mr.  W.  F.  Gardner,  the  instrument-maker  attached  to  the  Observatory, 
for  the  interest  he  took  in  pushing  the  work  forward  to  completion  in  the  very  limited  time  at  our 
disposal.  As  this  instrument  was  used  almost  solely  by  Dr.  Curtis,  it  is  unnecessary  to  enter  into 
details  respecting  it  here.  A  full  description  of  it  will  be  found  in  his  report. 

The  remaining  instruments  in  this  list  are  all  my  own  private  property. 

An  Achromatic  Telescope  of  43.58  inches  focal  length,  and  3.01  inches  clear  aperture,  made  by 


OBSERVATIONS    OF    THE    ECLIPSE    OF   AUGUST    7,  ldt>9.  ~27 

Alvan  Clark  and  Sons,  of  Cambridg»port,  Massachusetts.  This  instrument,  which  is  a  remarkably 
fine  oiie,  is  provided  with  a  terrestrial  eye-piece  magnifying  29.1  diameters,  and  with  Huygenian 
eye-pieces  magnifying  respectively  34.5,  05.5,  and  l.Ti.4  diameters.  It  is  equatorially  mounted  on 
a  very  firm,  portable  tripod  stand,  which  can  be  adjusted  to  any  latitude,  except  very  low  ones,  and 
has  a  slow  motion  by  which  it  may  be  moved  through  a  few  degrees  in  azimuth.  The  polar  and 
declination  axes  are  both  provided  with  clamp  screws,  but  there  are  neither  divided  circles  nor  tan- 
gent screws. 

Its  finder  has  a  focal  length  of  <S.O!I  inches,  and  a  clear  aperture  of  0.08  inches,  and  is  provided 
with  two  eye-pieces:  a  direct  one  magnifying  10.0  diameters,  and  a  diagonal  one  magnifying  0.2 
diameters.  Each  of  these  eye-pieces  has  a  Held  of  view  3°  20'  in  diameter.  The  finder  is  firmly 
fastened  to  the  telescope  tube,  and  is  not  capable  of  any  adjustment  whatever.  It  originally  car- 
ried in  its  field  of  view  a  pair  of  thick  cross-wires,  whose  position  was  so  near  correct  that  when  a 
star  was  brought  to  their  intersection  it  was  always  visible  in  the  field  of  view  of  the  telescope,  even 
with  the  highest  eye-piece.  When  I  decided  to  use  the  telescope  for  spectroscopic  work,  it  became 
necessary  to  have  more  delicate  means  of  pointing.  I  therefore  had  the  thick  cross- wires  removed, 
and  a  common  sewing  needle,  whose  point  can  be  placed  and  fastened  in  any  part  of  the  field  of 
view,  inserted  in  their  place.  It  is  easily  adjusted,  and  has  proved  very  satisfactory ;  the  image  of 
the  object  to  be  observed  being  readily  brought  upon  the  slit  of  the  spectroscope  by  bringing  its 
image  in  the  finder  just  into  contact  with  the  point  of  the  needle. 

A  Sinr/lc-prixm  ttyectroscope. — This  instrument  was  originally  made  by  P.  Desaga,  of  Heidelberg, 
and  was  intended  to  be  used  only  for  chemical  purposes,  but  J  have  had  great  alterations  and  addi- 
tions  made  in  almost  all  its  details,  so  that  it  can  now  be  employed  with  equal  facility  for  either 
chemical  or  astronomical  purposes.  It  is  shown,  arranged  for  astronomical  observation  and  attached 
to  the  telescope,  in  Plate  IV.  It  consists  of  a  central  brass  box,  which  contains  the  prism,  and  from 
which  radiate  three  tubes  of  unequal  sizes.  In  order  to  connect  the  instrument  to  the  telescope, 
the  end  of  the  largest  of  these  tubes  is  slipped  into  an  adapter,  and  fastened  there  by  means  of  a 
clamp  screw,  not  shown  in  the  plate.  Inside  of,  and  concentric  with,  this  large  tube  is  a  smaller 
one,  carrying  at  the  end  which  terminates  in  the  prism  box  an  achromatic  collimating  leus,  and  at 
its  other  extremity,  in  the  principal  focus  of  the  collimating  lens,  a  slit,  the  width  of  which  can  be 
varied  at  pleasure  by  means  of  a  screw  motion.  The  principle  upon  which  this  slit  is  constructed 
will  be  easily  understood  by  examining  the  diagram,  Fig.  1,  where  a  and  b  are  Fig.  1. 

the  two  jaws  of  the  slit,  which  are  constantly  pressed  together  by  the  springs 
shown  at  their  ends ;  c  is-a  wedge-shaped  piece  of  brass,  lying  above  the  jaws, 
and  having  a  rectangular  opening  in  its  center  to  permit  the  light  to  pass  to 
them.  This  wedge  can  be -moved  lengthwise  by  means  of  a  screw;  and  two 
pins,  one  inserted  in  each  jaw,  rest  against  its  sides.  When  the  wedge  is 
moved  downward  it  presses  against  these  pins  and  causes  the  jaws  to  open ; 
when  it  is  moved  upward  it  releases  the  pins  and  the  springs  press  the  jaws  closer  together.  The 
jaws  always  open  or  close  equally  on  each  side  of  the  slit,  so  that  the  position  of  the  middle  point 
bet  ween  them  is  constant.  This  is  a  matter  of  some  importance,  because  generally  the  thickness  of 
a  line  in  the  spectrum  is  precisely  equal  to  the  angular  opening  of  the  slit,  and  if  the  slit  were  to 
open  from  one  side  only,  the  lines  in  the  spectrum  would  widen  upon  one  side  only,  thus  shifting 
the  absolute  position  of  their  centers.  Another  of  the  tubes  radiating  from  the  prism  box  is  a 
small  achromatic  telescope,  the  eye-piece  of  which  is  provided  with  a  number  of  shade  glasses  of 
different  colors,  any  one  of  which  may  be  used  to  protect  the  eye  when  viewing  the  solar  spectrum. 
The  remaining  tube  which  radiates  from  the  prism  box  contains,  at  the  end  which  terminates  in  the 
box,  an  achromatic  collimatiug  lens,  and  at  its  other  end,  in  the  principal  focus  of  the  collimating 
lens,  a  very  finely  graduated  photographed  scale  of  equal  parts. 

The  action  of  the  instrument  is  as  follows:  Having  been  attached  to  the  sliding  tube  at  the 
eye  end  of  the  forty-three  inch  telescope,  that  tube  is  moved  out  or  in,  by  means  of  its  rack  work, 
until  the  slit  of  the  spectroscope  is  placed  precisely  in  the  principal  focus  of  the  object  glass.  Then 
the  sliding  tube  is  firmly  clamped,  and  the  telescope  being  directed  to  any  object,  the  spectrum  of 
which  it  is  desired  to  examine,  the  image  of  that  object  is  made  to  fall  within  the  jaws  of  the  slit. 
The  rays  of  light,  after  passing  through  the  slit,  fall  upon  its  collimatiug  lens  and  are  rendered  per- 
fectly parallel.  Then  impinging  upon  the  prism,  they  sutler  refraction  and  dispersion  in  their  pas- 


2B  REPORT    OF   PROFESSOR    HARKNESS. 

sage  through  it,  and  finally,  reaching  the  object  glass  of  the  small  telescope,  the  ra,vs  of  each  degree 
of  refrangibility  are  brought  to  a  separate  focus  by  it,  and  arc  seen  spread  out  into  a  spectrum  when 
viewed  through  its  eye-piece.  The  rays  of  light  proceeding  from  the  photographed  scale  are  ren 
dered  parallel  by  its  colliinating  lens;  then  falling  upon  the  second  face  of  the  prism,  are  reflected 
from  it  to  the  object  glass  of  the  small  telescope,  and,  passing  through  it,  are  brought  to  a  focus 
and  form  an  image  of  the  scale  precisely  at  the.  same  spot  where  the  rays  from  the  slit  form  the 
spectrum.  Therefore,  on  looking  into  the  small  telescope  the  spectrum  and  the  scale  are  seen 
together,  and  it  serves  as  a  micrometer  to  measure  the  position  of  the  lines  in  the  spectrum. 

The  scale  is  furnished  with  an  adjusting  screw,  by  means  of  which  its  fiftieth  division  can  be 
made  to  coincide  accurately  with  the  sodium  line.  How  to  illuminate  the  scale  properly  in  all  posi- 
tions of  the  large  telescope  was  a  problem  which  cost  me  much  thought,  but  I  finally  succeeded  in 
devising  the  following  arrangement,  which  has  proved  quite  satisfactory  :  The  tube  which  carries 
the  scale  and  its  collimating  lens  is  embraced  by  a  clamp,  which  can  be  fixed  in  any  required  posi- 
tion, and  from  which  extends  a  long  curved  arm  projecting  some  distance  beyond  the  plane  .of  the 
scale.  At  the  end  of  this  arm  is  a  brass  ball  pierced  with  a  socket,  the  produced  axis  of  which 
passes  through,  and  is  at  right  angles  to,  the  produced  axis  of  the  tube  which  carries  the  scale  and 
its  collimating  lens.  Tn  this  socket  is  an  axis  which  carries  a  bent  arm,  in  one  extremity  of  which 
a  lantern  swings  suspended  between  two  points,  and  in  the  other  extremity  a  rod  (which  is  in  the 
produced  axis  of  the  socket  in  the  ball)  slides  back  and  forward,  carrying  at  its  end  a  reflector 
inclined  at  an  angle  of  forty:five  degrees  to  the  rod.  Now,  let  the  position  of  the  spectroscope  be 
what  it  will,  the  clamp  can  be  loosened  and  turned  on  the  lube  which  carries  the  scale  until  the 
axis  of  the  socket  in  the  ball  is  horizontal.  Then  the  lantern  can  be  placed  vertically  by  moving  it 
on  its  pivots,  and,  if  necessary,  turning  in  its  socket  the  axis  which  carries  the  bent  arm.  Such 
being  the  state  of  affairs,  the  light  from  the  lantern  will  intersect,  at  right  angles,  the  produced 
axis  of  the  tube  which  carries  the  scale,  and  by  placing  the  inclined  reflector  in  the  proper  position 
it  will  be  thrown  directly  down  that  tube,  and  on  looking  into  the  small  telescope  the  scale  will  be 
seen  properly  illuminated.  The  lantern  itself  is  of  the  form  devised  by  3Ir.  Joseph  A.  Rogers,  of 
the  Hydrographic  Office,  and  is  fitted  to  burn  a  fluid  composed  of  four  volumes  of  alcohol  mixed 
with  one  volume  of  spirits  of  turpentine. 

The  adapter, by  which  the  spectroscope  is  attached  to  the  telescope,  has  a  motion  of  revolution 
around  its  axis,  by  means  of  which  the  slit  of  the  spectroscope  can  be  placed  at  any  desired  angle 
with  a  circle  of  right  ascension,  and  then  it  can  be  firmly  fixed  there  by  a  clamp-scre\v  which  is  pro- 
vided for  that  purpose.  There  is  also  a  hole  in  the  side  of  the  adapter  which  permits  light  to  fall 
on  a  small  equilateral  prism  placed  over  one  half  the  length  of  the  slit  of  the  spectroscope,  thus  fur- 
nishing the  means  of  comparing  the  spectrum  of  the  object  to  which  the  telescope  is  directed  with 
that  of  any  known  chemical  element. 

The  following  are  the  constants  relating  to  this  instrument : 

Small  telescope: 

Focal  distance  of  object  glass  6.55  inches. 

Clear  aperture  of  object,  glass  O.Si;  inch. 

Diameter  of  field  of  view  5°  •">•'•' 

.Magnifying  power  5.71  diameters. 

Collimating  lens  for  slit : 

Focal  distance  "••"•'-'  inches. 

Clear  aperture  0.82  inch. 

Collimating  lens  for  scale : 

Focal  distance  1-'^  inches. 

Clear  aperture  0.82  inch. 

Prism : 

Refracting  angle  M°    8' 

Minimum  deviation  of  line  D  47°  44' 

Refractive  index 
Density  -  3.532 


OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST    7,    1869. 


29 


In  order  to  give  breadth  to  the  spectrum  of  a  star,  there  is  a  plano-convex  cylindrical  lens,  0.65 
of  an  inch  square,  with  ;i  t'oeal  length  of  11.5  inches,  which  can  be  inserted  in  the  adapter. 

The  micrometer  scale  is  photographed  on  glass  in  such  a  manner  as  to  show  bright  lines  on  a 
dark  ground.  It  has  tour  hundred  and  twenty-one  divisions  to  an  inch,  whence  there  results  as  the 
value  of  a  single  division  0.002370  of  an  inch. 

Upon  a  careful  examination  the  graduation  proved  to  be  not  perfectly  regular,  and  the  follow- 
ing table  is  therefore  inserted,  which  gives  the  distance  from  the  zero  point  to  each  tenth  division, 
as  determined  from  measures  made  with  the  mural  circle: 


Division. 

Angular  distant  r. 

1 

Division. 

Angular  distance. 

o    ,    „ 

o   /   // 

0 

0   0   0 

110 

3  35  32 

10 

•  0  19  30 

120       3  55  10 

20 

0  39  13 

130  :     4  14  42 

30 

0  58  48 

140 

4  34  25 

40 

1  18  20 

150 

4  53  59 

50 

1  3?  15 

160 

5  13  21 

60 

1  57  '.'7 

170 

5  32  51 

70 

2  HI  .->:; 

180 

5  52  28 

80 

2  36  17 

190 

6  11  56 

90 

2  55  55 

200 

6  31  19 

100 

3  lo  :'.() 

The  mean  value  of  one  division  is,  therefore, 

1'  57" A 
and  the  corrections  necessary  to  free  the  scale  from  the  effect  of  irregularity  of  division  are  as  follows: 


Division. 

Correction. 

Division. 

Correction. 

Division. 

Correct  ion. 

0 

H 
II 

70 

+     5 

140 

-  29 

10 

+  4 

80 

+  15 

150 

-  29 

20 

—  5 

90 

+  H 

160 

-  17 

so 

—  6 

100 

+     4 

170 

-  13 

40 

-  4 

110 

-  18 

180 

-  16 

50 

+  5 

120 

—  22 

190 

-  10 

60 

—  3 

130 

—  20 

200 

+     1 

In  order  to  render  the  scale  of  this  instrument  comparable  with  those  of  others,  we  have  the 
data  contained  in  the  following  table,  the  first  column  of  which  gives  the  designation  of  the  line  in 
the  spectrum  ;  the  second  column  the  scale-reading  of  this  instrument;  the  third  column  the  read- 
ing of  Kirchhoff's  scale;  and  the  fourth  column  the  wave  length  expressed  in  millionth  a  of  a  mil- 
limeter. The  readings  given  for  the  line  D  correspond  to  the  mean  of  the  two  sodium  lines,  and 
those  given  for  6  correspond  to  the  mean  of  the  three  magnesium  lines,  giving  double  weight  to  the 
least  refrangible  line.  Beyond  the  line  G- the  readings  given  in  the  column  belonging  to  Kirch- 
hoff's scale  are  those  of  Angstrom's  and  Thalen's  continuation  of  Kirchhoff's  map : 


Lino. 

Scalr  II. 

Si-ale  K. 

Wave  trust  li. 

Line. 

Scale  H. 

Seal,:  K. 

\\"n\e  length. 

a 

26.9 

503 

1> 

71.5 

1643 

518.1 

B 

31.5 

sea 

687.5 

F 

84.8 

2080 

4*6.  :, 

C 

36.2 

694 

656.  8 

G 

117.8 

2855 

431.0 

D 

50.0 

1005 

589.7 

H, 

146.5 

8778 

397.2 

E 

67.  9 

1524 

527.4 

H, 

150.5 

3882 

393.  (i 

30 


REPORT  OF  PROFESSOR  HARKNF.SS. 


By  means  of  a  graphical  interpolation  I  have  obtained  from  these  data  the  reading  of  Kirch - 
hoif's  scale,  and  the  wave  length,  for  every  fifth  division  of  the  scale  of  my  instrument,  as  given  in 
the  following  table : 


Scale  H. 

Scale  K. 

Wave  length. 

Scale  H. 

Scale  K. 

Wave  length. 

25 

462 

. 

95 

2335 

467.  2 

30 

560 

700.0 

100 

2445 

168,3 

35 

665 

664.2 

105 

2560 

449.9 

40 

772 

636.2 

110 

2675 

442.  1 

-45 

885 

611.8 

115 

2788 

l:;i.  - 

50 

1005 

589.8 

120 

2925 

428.0 

55 

1135 

569.8 

125 

3095 

i2i.»; 

60 

1278 

551.8 

130 

3262 

415.  r> 

65 

1432 

535.8 

135 

:;  1  K 

409.  7 

70 

1595 

521.  4 

140 

3590 

404.2 

75 

1760 

508.5 

145 

3735 

399.0 

80 

1920 

497.0 

150 

3868 

394.1 

85 

20&5 

486.5 

166 

3896 

389.5. 

90 

2218 

476.6 

Under  favorable  conditions  this  spectroscope  will  show  the  line  I)  in  the  solar  spectrum  dis- 
tinctly double. 

An  Arago  Polar  iscope,  consisting  of  a  plate  of  quartz  cut  perpendicularly  to  the  axis,  and  a 
double-image  prism,  giving  images  of  complementary  colors  when  polarized  light  is  present. 

A  Savart  Polariscope,  consisting  of  a  plate  of  quartz  cut  obliquely  to  the  axis,  and  a  plate  of 
tourmaline,  giving  Savart's  bands  when  polarized  light  is  present. 

A  Sextant,  made  by  Stackpole&  Brother,  of  New  York,  from  my  own  designs,  marked  No.  937, 
of  six  inches  radius,  divided  on  platina,  and  reading  to  ten  seconds,  having  a  telescope  of  5.32  inches 
focus  and  0.89  inch  clear  aperture,  provided  with  eye-pieces  magnifying  respectively  2.75,  5.66,  and 
8.88  diameters.  Attached  to  the  index  bar  is  a  finding-level,  which  proved  a  very  great  coin  e 
nience  and  saved  much  time  and  trouble. 

If  we  let  E  represent  the  correction  necessary  to  free  any  measured  angle,  u>,  from  the  eft'ect  of 
eccentricity  of  the  sextant,  and  («•)  represent  the  reading  of  the  point  oil  the  arc  where  the  divisions 
of  the  limb  and  vernier  coincided  when  the  angle  u>  was  measured,  then 

E  =  2  e .  sin  ±(<o).  cos  [a  +  £  (<«)] 

«  and  e  being  constants  which  must  be  determined  from  the  measurement  of  known  angles.  The 
quantity  a  is  the  angle  included  by  the  two  lines  passing,  respectively,  from  the  center  of  the  divided 
arc  to  the  zero  .point  on  the  limb,  and  from  the  center  of  the  divided  arc  to  the  center  on  which  the 
index  bar  turns.  For  the  quantity  e  we  have 

2b 


II.  sin  1" 

in  which  b  is  the  distance  from  the  center  of  the  divided  arc  to  the  center  on  which  the  index  bar 
turns,  and  K  is  the  radius  of  the  divided  arc. 

After  my  return  from  Ues  Moines,  from  the  measurement  of  seventeen  known  angles,  included 
between  the  limits  34°  22'  and  112°  20',  I  found,  by  the  method  of  least  squares,  for  the  sextant 
under  consideration 


«  =  114°  4 

2e=   62".5 


OBSERVATIONS   OF   THE   ECLIPSE    OF    AUGUST   7.    1869. 


31 


and  by  moans  of  the  formula  given  above  I  have  computed  from  these  values  the  following  table 
of  the  corrections  which  must  be  applied  to  angles  measured  with  this  instrument  in  order  to  free 
them  from  the  effects  of  eccentricity. 


lit 

E 

" 

E 

6) 

E 

0 

II 

o 

II 

O 

II 

0 

0.0 

60 

+   S.I 

100 

+  19.9 

10 

+   1.2 

60 

+  10.2 

110 

+  22.  G 

20 

+   2.0 

70 

+  12.  5 

120 

+  25.3 

30 

+   4.3 

80   !+  14.  9 

130 

+  28.0 

40 

+   (5.1 

90 

+  17.4 

140 

+  30.  8 

A  Mercurial  Artificial  ll<>r!:oit.  marked  Ha.  1,  having  a  folding  roof,  and  an  iron  trough,  three 
inches  wide  by  five  inches  long. 

If  («  is  the  double  altitude  of  an  object  seen  in  au  artificial  horizon  ;  /*  the  index  of  refraction  of 
the  glass  composing  the  roof  of  the  horizon;  x  a  constant  peculiar  to  the  roof  which  is  employed 
and  which  must  be  determined  from  observations  made  for  that  .purpose  ;  then,  assuming  /i  =  1.514, 
the  correction  necessary  to  free  any  observed  angle  from  the  error  introduced  by  a  prismatic  form 
of  one  or  both  of  the  glasses  composing  the  roof  of  the  horizon  will  be  given  by  the  expression 


'  ( 


1 


/""  —  sin2  (45°  --~ 
"cos  (450  —  4  w) 


The  value  of  the  co  eflicient  of  /.,  for  values  of  <«  ranging  between  30°  and  15(1°,  is  given  in  the, 
following  table  : 


u 

u 

<j 

u 

o 

0 

0 

o 

30 

0.  fi502 

ISO 

55 

0.5559 

125 

35 

.  <;•,'.->:> 

145 

60 

.5444 

120 

40 

.  f.04l 

140 

70 

.  5273 

110 

45 

.  5855 

135 

80 

.  5173 

100 

BO 

.  5C.95 

130 

90 

.  5140 

90 

From  three  sets  ;>f  observations  of  Polaris  reflected,  made  with  the  mural  circle  belonging  to 
this  Observatory,  and  the  horizon  Ha.  1,  each  set  consisting  of  five  readings  of  the  micrometer 
with-the  side  A  of  the  horizon  roof  next  the  observer,  and  live  readings  with  the  side  B  next  the 
observer,  I  found  that  when  the  side  A  was  next  the  observer  the  star  appeared  too  high  by  the  fol- 
lowing quantities: 

0".285 
.207 
.21!) 


.Mean  =  0.237 

As  the  double  altitude  of  Polaris  at  the  time  of  observation  was  80°  34',  the  co-efficient  of; 
was  0.5171.     Hence  we  have: 


32 


REPORT    OP   PROFESSOR    HARKNESS. 


The  corrections  to  be  applied  to  double  altitudes  measured  with  this  horizon,  for  Tallies  of 
between  30°  and  150°,  are  therefore  as  follows : 


tf 

C'orr. 

u 

u 

COIT. 

u 

o 

a 

^ 

o 

// 

tj 

30 

0.30 

150 

70 

0.24 

110 

40 

.28 

140 

80 

.24 

100 

50 

.20 

130 

90 

0.24 

90 

CO 

0.25 

120 

These  corrections  are  to  be  subtracted  from  double  altitudes  measured  with  the  side  A  of  the 
roof  next  the  observer,  and  added  to  double  altitudes  measured  with  the  side  B  next  the  observer. 
However,  they  will  never  change  the  resulting  single  altitude  by  more  than  0".15,  and,  as  that  is  a 
quantity  utterly  unappreciable  with  a  sextant,  this  roof  may  be  considered  as  perfect. 

A  Pocket  Sextant,  made  by  Stackpole  and  Brother,  of  New  York,  marked  No.  .'546,  having  an  arc 
of  two  and  a  quarter  inches  radius,  and  reading  to  single  minutes. 

A  Black  Glass  Artificial  Horizon,  four  inches  long  by  three  inches  wide,  provided  with  a  very  sen- 
sitive level,  and  an  inclined  plane  with  black  glass  surfaces  which  can  be  set  on  the  horizon  for  the 
purpose  of  measuring  zenith  distances  ranging  between  seventy  and  one  hundred  and  thirty  degrees. 

A  Prismatic  Compass,  having  colored  glasses  for  the  purpose  of  observing  the  sun,  and  a  needle 
three  inches  long,  carrying  a  metal  circle  three  inches  in  diameter,  divided  to  single  degrees. 

A  Small  Reflecting  Lerel. 

A  Pocket  Compass. 

A  Fifty-foot  Chesterman''s  Metallic  Tape  Measure,  which  had  been  carefully  tested,  by  means  of 
an  eighteen-inch  steel  standard  rule,  and  found  to  be  correct. 

A  Binocular  Field  Glass,  magnifying  5.50  diameters  and  having  a  Held  of  view  of  2°  50'. 

A  Pocket  Achromatic  Telescope,  having  an  object  glass  made  by  Alvan  Clark  and  Sons,  of  9.99 
inches  focus  and  1.09  inches  clear  aperture,  with  a  terrestrial  eye-piece  magnifying  19.2  diameters 
and  a  field  of  view  of  1°  48';  provided  with  a  screw  clip  for  holding  it  steadily  while  observing. 

A  Set  of  Three  Colored  Glasses,  mounted  in  a  horn  frame  for  the  pocket. 

A  Pocket  Thermometer. 

A  Rain  Gauge,  having  a  receiving  surface  2.788  inches  in  diameter,  and  a  glass  measure  for  the 
same,  holding  half  an  inch  of  rain  and  graduated  to  each  0.005  of  an  inch. 

A  Break-circuit  Telegraph  Key. 

A  Set  of  Drawing  Instrument's. 

We  had  with  us,  for  the  use  of  the  party,  three  mean-time  box  chronometers,  made  by  T.  S.  and 
,T.  1).  Negus,  of  New  York,  a  full  account  of  which  will  be  found  in  Professor  Eastman's  report. 

I  had  also  the  following  articles:  American  Nautical  Almanac,  and  supplement,  for  1869; 
Chauvenet's  Astronomy ;  Loomis's  Practical  Astronomy ;  Chauvenef  s  Trigonometry ;  Four-figure 
Logarithms ;  Bowditch's  Useful  Tables ;  Bremiker's  Six-figure  Logarithms ;  Crelle's  Multiplication 
Table ;  Star  Maps ;  scale  of  tints  with  which  to  compare  the  colors  of  the  protuberances  around  the 
sun  during  the  totality;  blank  forms  for  latitude  and  time  observations;  blanks  for  spectroscope 
observations. 

GENERAL  REMARKS  ON  THE  OBSERVATIONS  FOR  TIME  AND  LATITUDE. 

The  observations  for  time  and  latitude  were  all  made  by  me,  assisted  either  by  Professor  East- 
man or  Dr.  Curtis,  one  of  whom  always  noted  the  time  at  a  given  signal,  and  then  recorded  the 
observation.  Under  the  circumstances,  I  considered  that  method  as  accurate,  and  certainly  much 
more  convenient,  than  it  would  have  been  for  me  to  have  taken  up  the  beat  of  the  chronometer  and 
noted  the  time  myself.  The  instruments  employed  were  the  sextant  Stackpole  and  Brother,  No.  937, 
with  a  magnifying  power  of  8.88  diameters  on  the  telescope ;  the  mercurial  artificial  horizon  Ha.  1 ; 
and  the  mean-time  chronometer  T.  S.  and  J.  D.  Negus,  No.  1319.  At  night  the  index  correction  of 
the  sextant  was  determined  by  observing  the  coincidence  of  the  direct  and  reflected  image  of  a  star; 
in  the  day-time  it  was  determined  by  measuring  the  diameter  of  the  sun  both  on  and  off  the  arc. 
In  order  to  avoid  reading  tbe  vernier  backward  on  the  arc  of  excess,  which  always  involves  risk 


1809.  33 

of  error,  tin-  zero  of  Mio  graduation  was  taken  at  a  point  live  degrees  oft'  the  are.  Thus  an  angle 
recorded  as  4°  li.V  50"  was  really  34'  10"  oft'  the  are.  This  applies  only  to  angles  measured  on  the 
arc  of  excess  for  the'  purpose  of  determining  index  corrections. 

The  refractions  have,  been  computed  by  means  of  Hessel's  formula,  sometimes  using  the  tallies 
given  in  the  appendix  to  the  Washington  observations  for  1845,  and  sometimes  those  given  in 
Loomis's  Practical  Astronomy  ;  from  which  latter  book  all  reductions  to  the  meridian  have  also 
been  taken.  Itight  ascensions,  declinations,  parallaxes,  semi-diameters,  and  all  other  elements  of 
the  lieavenh  bodies  which  were  required  in  the  reductions,  have  been  taken  from  the  American 
Nautical  Almanac. 

OBSERVATIONS  FOE  TIME. 

All  observations  for  time  have  been  made  on  the  sun  in  the  following  manner  :  Suppose  the  sun 
to  be  rising.  The  index  of  the  sextant  was  set  at  an  angle  a  little  greater  than  the.  double,  altitude 
of  the  upper  limb  ;  the  angle  chosen  being  always  at  some  whole  degree,  or  else  at  some  15',  30',  or 
45',  on  the  graduated  are.  Then,  looking  through  the  telescope  of  the  sextant  into  the  artificial 
horizon,  the  two  images  of  the  sun  were  seen  separated,  but  approaching  each  other,  and  the  instant 
when  the  two  limbs  came  into  contact  was  noted.  The  index  was  then  set  forward  fifteen  minutes, 
and  the  same  process  repeated;  after  whicJi  it  was  again  set  forward  lift  ecu  minutes  more,  and  the 
same  process  repeated  a  third  time;  thus  giving  three,  observed  contacts  of  the  upper  limbs.  The 
roof  of  the  artificial  horizon  was  next  reversed,  and  the  index  of  the  sextant  set  back  to  its  first 
reading.  Then,  looking  through  the  telescope  of  the  sextant  into  the  artificial  horizon,  the  two 
images  were  seen  overlapping,  but  separating,  and  the  instant  of  last  contact  of  the  two  limbs  was 
noted.  The  index  was  then  set  forward  fifteen  minutes,  and  the  same  process  repeated  ;  after  which 
it  was  again  set  forward  fifteen  minutes  more,  and  the  same  process  repeated  a  third  time;  thus 
giving  three  observed  contacts  of  the  lower  limbs  respectively  at  precisely  the  same  altitudes  as  the 
corresponding  ones  of  the  upper  limbs.  If  the  sun  was  falling,  instead  of  rising,  then  the  same 
observations  were  made,  but  their  order  was  reversed.  The  advantage  gained  by  observing  in  this 
manner  is  that  all  correction  for  semi-diameter  is  avoided,  all  errors  arising  from  a  prismatic  form 
of  the  glasses  in  the  roof  of  the  artificial  horizon  are  eliminated,  and  even  for  a  very  accurate  reduc- 
tion there  is  needed  only  a  single  computation  of  the  refraction. 

The  reduction  of  observations  for  time  has  been  effected  by  means  of  the  following  formula1  : 


a 


> 

—  r  +  p  i.  s 


sin 


=  A/8"1  (^  —  rt)  '  cos  ^  '  s«c  <p  .  cosec  d 


In  which 

T  =  mean  of  observed  chronometer  times. 

{2  =  mean  of  observed  double  altitudes. 

01  =  correction  for  index  error,  eccentricity,  &c. 

r  =  refraction. 

p  =  parallax. 

it  =  semi-diameter. 

a  =  the  geocentric  altitude  of  the  center  of  the  object  observed. 

d  =  polar  distance  of  object  observed,  measured  from  the  elevated  pole. 

y  =  latitude  of  place  where  observation  is  made. 
tf  =  hour  angle,  at  the  pole,  of  the  object  observed. 

T==  equation  of  time. 
<Zt=  correction  of  the  chronometer  to  reduce  the  reading  of  its  face  to  local  mean  time. 

Appended  is  a  specimen  of  the  form  upon  which  the  observations  were  recorded  and  reduced. 

Most  of  it  will  be  sufficiently  intelligible  without  any  explanation.     Under  the  head,  "Index  cor- 

rection, &c.,"  the  columns  "On  arc"  and  "Off  arc"  are  used  when  the  index  correction  is  deter 

mined  from  the  sun  ;  that  headed  "  Coincidence  of  images"  when  it  is  determined  by  observing  a  star. 

5* 


34 


REPORT   OF   PROFESSOR    HARKNESS. 


With  some  instruments  it  is  possible  that  the  measures  of  the  sun's  diameter  made  on  and  off  the 
arc  may  require  correction  for  eccentricity.  In  such  a  case  the  correction  is  inserted  on  the  line 
"Eccentricity,"  and  by  adding  it  to  \  (<«'  —  <«)  the  true  index  correction  is  obt-ained.  The  quanti- 
ties rh  <7,  B,  F,  and 'Art.  Hor.,  are  all  functions  of,  and  vary  with,  the  measured  angle  to  which  the 
index  correction  is  to  be  applied.  (In  this  example  84°  -t.5f.)  rt  is  the  correction  for  want  of  paral- 
lelism between  the  line  of  sight  of  the  telescope  and  the  plane  of  the  sextant;  a  is  the  correction 
for  a  prismatic  form  of  the  index  glass;  E  is  the  correction  for  eccentricity,  a  table  of  which  for  this 
instrument  is  given  on  page  31 ;  F  is  the  correction  for  a  change  of  index  error  dependent  upon  the 
position  in  which  the  sextant  is  held,  or  in  other  words,  for  flexure;  Art.  Hor.  is  the  correction  for 
want  of  parallelism  in  the  surfaces  of  the  glass  composing  the  roof  of  the  horizon ;  a  table  of  its 
values  for  the  horizon  Ha.  1  is  given  on  page  32,  but  when,  as  in  the  present  case,  half  the  observa- 
tions have  been  taken  with  the  roof  in  one  position,  and  the  other  half  with  it  reversed,  the  error 
eliminates  itself  and  the  correction  is  zero. 

Observations  for 

SMioii,  DCS  Moiiies,  Iowa 

Instrument,  Sextant  - 

Artfticial  Horizon 

Chronometer 

Observer,  Wm.  Harkness   - 


Time. 

Date,  August  1, 
M<u'l;t>»lr  <(•  />Vo.,  No.  937. 
Folding  Mercurial,  Ha.  1 
T.  &  &  J.  D.  Nfym,  So.  1319. 
Object,  »S'i<n. 


•  Double  Altitude. 

Limb 

observed. 

jj 

Chronometer. 

o             in 
85          0          0 

0 

A 

h.        in.           *. 
9        30          8.  5 

84        45          0 

U 

U 

30         .M..-> 

84        30          0 

u 

11 

31        33.  6 

85          0          0 

© 

B 

33          5.  0 

84        45          0 

tt 

" 

33        47.  1 

Sums. 
Means. 
Index  Corr.,  &c. 
Q 

84        30          0 

" 

u 

34         29.  4 

. 

13        55.1 

84        45          0.  0 
4-    2        31.  1 

9        32        19.2 

Thermometer        74.0 

84        47        31.  1 

in 

42        23        45.  5 

Barometer              29.  7(i 

Retraction. 

59.  5 

At,  Thor. 

Parallax. 

-f-               6.3 

Semi-diam. 



42        22        52. 

d 

73         44         59. 

2S 
S 

41         35        :«!. 

157        43        27 

78        51        44 

S  —  « 

S6        28        52 

o         i          a 
-f     Hi       15      0.6 

Declination  of  object 

Polar  distance  of  object                                                      73       44     59.4 

OBSERVATIONS   OF   THE    ECLIPSE    OF   AUGUST   7,    1309. 


35 


Ottfeot 

Index  Correction,  &c. 

On  are  =  u 

Off  arc  =  u' 

Coincidence  of 
Images. 

Sums. 
Means. 

w'  —  <j 
i  (u'  —  u) 
Eccentricity 
Index  Corr. 
;;  anil  c 
E 
F 
Art.  Hor. 
Index  Corr.,  &c. 

t           it 

20      :so 

25 
25 

O               '               " 

4        20        5 
0 
5 

/           // 

80 

10 

29        26.  7 
33        511.  7 

4        20        3.  3 

Sin  (S  —  a) 
CosS 
Sec  <j> 
Cosec  d 
Sin*  i  H 
Sin  |  II 

Logarithms. 

+    4       :',<).  o 

9.774194 
9.  285937 
.126171 
.  017707 

+     2         15.  0 
0.0 

+     2         15.  0 
0.0 
+  10.1 
0.0 
0.0 

9.  204009 

9.  602004 

/ 

li.      m.          s. 
3        8        36.0 

+  5        2f>.2 

+    2        31.1 

Local  Apparent  Time 

314          2.  2 
9      32        19.2 

Time  liy  Clironoinetei 

Chronometer  t'asf  nf  1 
Longitude  west  of  \Vi 

Chronometer  fast  of-  \ 
These  oliscrvatk 

0.  38  of  an  inch  inn* 
from  index  error. 

ocal  Mean  Time  

6      18        17.  0 
1        6        16.  0 

Washington  Mean  T 
us  were  made  after 

t  In1  subtracted  t'rni 

5      12          1.  0 

noon. 
n  tin'  rending  of  the  barometer  to  free  it 

The  observations  for  time  are  given  in  detail  in  Schedule  A,  appended  to  this  report,  but  for 
con vcn fence  of  reference  the  following  .abstract  of  them  is  inserted  here.  The  column  headed 
"  Mean"  is  the  menu  of  the  forenoon  and  the  afternoon  observations,  and  is  taken  to  be  the  error  of 
the  chronometer  at  noon.  In  cases  where  (here  is  only  one  set  of  observations  in  the  forenoon,  and 
two  sets  in  the  afternoon,  in  taking-  the  mean  1  have  given  the  morning  observations  double  weight, 
because  there  seems  to  be  a  constant  difference  between  them  and  the  afternoon  ones. 


36 


REPORT   OF   PROFESSOR   HARKNESS. 
Chronometer  T.  8.  &  J.  D.  Negus  No.  1,319,  fast  of  Dot  Mo!  in* 


time,  by  obxercutiou. 


Date. 

A.M.          P.M. 

Menu. 

1,'nily 
rate. 

Hourly 
rate. 

/I.     Wl.         *. 

8. 

/i.    in.      ». 

•-. 

8. 

July    93 

6    18    8.  4 

7.4 

6    18    8.0 

23 

7.9 

-  0.  47 

—  0.  020 

24 

8.9 

26 

9.8 

8.9 

9.4 

27 

10.6 

.    . 

. 

1.05 

.044 

27 

10.8 

28 

12.3 

10.7 

11.5 

. 

28 

10.9 

0.50 

.021 

29 

1-2.4 

11.8 

12.0 

29 

11-.  6 

. 

0.20 

.008 

30 

12.0 

12.6 

12.2 

30 

12.5 

11.9 

. 

1.40 

.058 

31 

13.8 

13.3 

13.  6 

31 

13.9 

13.6 

0.45 

.019 

Aug.     4 

15.1 

15.  7 

15.4 

—  0.  63 

—0.  026 

7 

17.2 

17.0 

17.3 

7 

17.9 

17.0 

. 

+  0.20 

+0.  008 

8 

6    18  16.9 

17.2 

6     1«  17.  1 

As  the  time  is  of  very  great  importance  on  the  day  of  the  eclipse,  I  have  obtained  the  chronom- 
eter error  employed  on  that  occasion,  as  follows  :  The  telegraphic  comparison  made  at  Des  Moines 
on  the  evening  of  August  7,  1869,  between  my  mean-time  chronometer,  T.  S.  and  J.  1).  Negus  No. 
1319,  and  the  Kesscls  sidereal  clock  at  Washington,  gave 

31,  4m  55».30,  Negus  =  19h  Om  Os.O,  Kessels. 
Then  we  have 

h.  HI.  8. 

Time  by  face  of  Kessels  19      0      0.00 

Kessels  fast  -        - 


27.16 


Washington  sidereal  time 
Sidereal  time  of  mean  moon 

Sidereal  interval 
Acceleration  on  mean  time 

Washington  mean  time 

Time  occupied  by  passage  of  signal  from  Washington  to  Des  Moines 

Des  Moines  west  of  Washington 

Des  Moines  mean  time 
Time  by  Negus,  1:519 

Negus  i:;i!»,  fast 
I  (ate  from  noon 

Negus  1."»I9,  last  at  noon    - 

At  the  time  of  the  eclipse  this  chronometer  was  therefore 

Qb  18"'  178.2fast 


18    59     32.84 


9 


1.50 


9     54  31.34 

1  37.40 

9     52  53.94 

+  0.21 

—     16  10.09 

8     46  38.06 

3      4  55.:  !0 

6     18  17.24 
0.10 

6     18  17.14 


OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST    7,    18C.9.  37 

of  DCS  .Monies  mean  time.  I  have  thought  it  best  to  determine  its  error  in  this  way  because  by  so 
doing  it  is  niiiile  to  depend  upon  seventeen  sets  of  time  observations,  instead  of  upon  four  sets,  as 
would  he  tin1  ease  if  the  observations  of  August  7  only  were  used.  For  an  explanation  of  the  rate 
employed  for  this  chronometer,  and  the  error  of  tbe  Kessels  clock,  see  pages  42  and  43. 

OIJSKItVATIONS  FOK  LATITUDE. 

Circum-meridian  altitudes  of  the.  sun  for  latitude  were  observed  as  follows:  Three  double  alti- 
tudes of  one  litnli  were  taken,  and  then  the  roof  of  the  artificial  horizon  was  reversed,  and  three 
double  altitudes  of  the  other  limb  observed.  Thus  the  semi-diameter  of  the  sun,  and  all  errors 
depending  upon  any  imperfection  of  the  roof  of  the  artiticial  horizon,  were  eliminated.  It  is  perhaps 
scarcely  necessary  to  add  that  the  time  was  noted  and  recorded  at  the  instaut  of  observing  each 
double  altitude.  ( 'ireum -meridian  altitudes  of  stars  were  observed  in  the  same  way  as  those  of  tbe 
sun,  except  that  the  coincidence  of  images  was  taken  instead  of  the  contact  of  limbs. 

The  reduction  of  the  observations  for  latitude  Las  been  effected  by  means  of  the  following 
formula- : 


*  -JT- 

]_    ]   ~  80400        J 
f  1  T 

fc»  =  ,)T — ;K 

SliKIO 


Log.  i  =  0.00237. 
When  the  sun  is  observed  with  a  mean-time  chronometer, 

,      COS  if.  COS" 
A  :=^  tC      - 

Sill  *| 

When  a  star  is  observed  with  a  mean-time  chronometer, 

.  .   COS  y.  COS  » 

A  =  KI. 

sin  Ci 

B  —  A-1,  col  :, 

2  sin2  i  t 

m=     .    ,  - 
sin  I" 


siiiT/7~ 


fi  =  »  +  >'  —  p  is  —  A  m  +  B  n 

<p=^  +  o 

In  which 

fl  =  niean  of  observed  double  altitudes. 
«  =  correction  for  index  error,  eccentricity,  &c. 
r  =  refraction. 
jj  =  parallax. 
a  —  semi-diameter. 

<5T==rate  of  chronometer  in  twenty-four  hours,  positive  when  the  chronometer  is  losing. 
•(5E=the  increase  of  the  equation  of  time  in  twenty  -fom  boors  ;  the  equation  of  time  being  regarded 

as  positive  \\hen  it  is  to  be  added  to  apparent  time. 
*  =  hour  angle  of  the  object  observed. 


38 


KEPOET    OF    PROFESSOR    IIARKNESS. 


<J  =  declination  of  the  object  observed;  north  declinations  being'  taken  positive.     For  a  culmina- 
tion below  the  pole,  it  must  be  measured  from  the  equator  through  the  zenith  to  the  object  : 
that  is,  it  is  equal  to  180°—  S. 
C  =  observed  zenith  distance  of  object,  which  is  to  be  taken  as  positive  when  the  object  is  south 

of  the  zenith. 

£,  =  true  geocentric  zenith  distance  of  the  object  at  the  time  of  its  culmination. 
y  =  latitude  of  the  place  of  observation. 

Appended  is  a  specimen  of  the  form  upon  which  the  observations  were  recorded  and  reduced. 
That  part  of  it  relating  to  the  index  correction  is  precisely  the  same  as  in  the  case  of  the  time 
observations,  and  the  remainder  of  it  will  be  sufficiently  intelligible,  without  any  explanation. 

Observations  for   Latitude. 

Station,  DCS  Moines,  Iowa  Date,  July  I'l,  1869. 

Instrument,  Sextant  -  Mackjmlc  it  Jiro.,  Xo.  937. 

Artificial  Horizon  Foldiiu/  Mercurial,  Ha.  1. 

Chronometer  T.  fl.  &  J.  D.  XMJUK  No.  1319. 

Observer,  Wm.  Hardness   -  Object,  Sun. 


Chronometer. 

Double  Altitude. 

* 

t. 

in.               a. 

/).          m.              X. 

6        7-51.5 

C             J              " 

136       17       45 

111.            X. 

16      29.  4 

533.6           0.7 

8        32.0                           20      10 

15       4H.  11 

I'.in.  ii            .6 

9          9.5                           22      20 

IT,       11.4 

45-,>.  9              .  5 

JO        11.3                135      23      10 

14         9.  6 

393.  6             .  4 

1(1        55.3 

25      10 

13      ;.';-,.(; 

:;.-,:',.  9           .  3 

12          7.  0 

29      30 

l->      1  ::.'.> 

29::.  7           .2 

58        .IH.Ci                           18        5 

Sums. 

251Ki;          2.7 

(i    "9        47.8 

i:;r>     r>3      0.8 
+    2      50.  5 

Mriins. 

119..-           0.45 

Index  Corr.,  &e. 
Q 

to 

90°  —  £Q  =  ? 

Thermometer,  86.0 

Barometer. 

At,  Ther. 

135      55      51.3 

67       57       55.  6 

22        2        4.4 

Kefraction 

+            21.7 

Parallax 

3.2 

Semi-diameter 



. 

A»I0 

-  13      14.5 

B»0 
fi 

+              4.0 

21      49.     12. 

<! 
«» 

+  19      46      24. 

/I.       Ml.        K. 
=     12    6     12.0 

6  18       8.9 

=     (;•>.)   -jo.  9 

41       35      36. 

Time  of  culmination 

Chronometer  lime  01 

OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST    7,    1869. 


Index  Correction,  &c. 

Oli.jrrl.                                Oil  air  —  (J 

Otf  arc  =  w' 

Ciiinciilciico  of 
Image's. 

/               // 
2l»             "> 

O            '                " 

•i     •><;      ii 

/          // 

in                           20 

in 
sum*.                                             2."-. 

Means.                                              '."I           8.3 
33        r>0.0 
u'  —  u                                      +     4        -11.7 

in 

30. 

4       «i       I".  l» 

. 

Sin  M 
Ar.  Conij). 

Logarithms. 

9.  5703 

H  "'-<•>)                       4-   2      20.8 

0.4297 

l.c  i  rntricity.                                              0.0 

Cos  <p 

9.  H?3- 

Index  (  'HIT.                             -f     1        20.  f 

(  'i.-  c 

n.;i7:{(i 

^  anil  T                                                        0.  0 

fc        • 

K                                                         +     29.7 
F                                                                   0.  0 

i 
A 

0.  2771 

Art.  lli.r.                                                     0.0 

>"o 
A/»0 

2.  62:«> 
2.  SMI01 

Imlrx  Corr.,  &c.                    +     a        r,0.  r> 

A- 

0.6542 

Ciil  fi 

0.  :!!I74 

H3 

B/^ 

'.1.  <i.r>32 

0.6048 

Ii.        in.        ». 
II        0         12.0 

1        (5         16.  0 

AsMiinnl  l,oiif{itii(lf  west  of  Washington 
BKMAK 

KS. 

Observations  tor  latitude  iimde  on  Polaris  when  at  a  considerable  distance  from  the  meridian 
have  been  reduced  by  means  of  the  formula 


<P  =  Ji  —  p.  cos  t  +  i  p2.  sin  1".  sin2  1.  tan 
In  which 

i2  =  mean  of  observed  double  altitudes. 
«i  =  correction  for  index  error,  eccentricity,  &c. 
r  =  refraction. 

jj=polar  distance  of  the  star,  expressed  in  seconds  of  arc. 
t=.=  honr  angle  of  the  star. 


40 


REPORT    OF    PROFESSOR    HARKNE8S. 


The  observations  for  latitude  are  given  in  detail  in  Schedule.  ]>,  appended  to  this  report,  but 
for  convenience  of  reference  the  following  abstract  of  them  is  inserted  here: 

Observations  for  Latitude  of  Temporary  Ohxerratory. 


Date. 

Object. 

I.;M  it  Ililr. 

1869. 

0          '          II 

July    23 

Sllll    

41   :ir.  •.':, 

23 

Sun  

84 

24 

Sun        

36 

25 

Sun  ....... 

29 

26 

Sun  

411 

27 

Sim 

29 

28 

Sun 

42 

28 

Sun 

35 

29 

Sun  

35 

29 

Sun 

33 

29 

37 

29 

:«) 

30 

Sun 

:;<; 

30 

Sun 

34 

30 

Polaris  

40 

31 

Sun 

•II 

31 

Sim 

:!'.) 

Ann      2 

Sun 

41 

2 

Sim  

41 

2 

a  Onliiuchi     .... 

33 

2 

Polaris  

26 

2 

a  Aqnilip  

1 

4 

<i  Sngittarii   .... 

48 

Rejecting  the  observation  of  a  Aquihe  made  on  August  2,  the  mean  of  all  the  observations  of 
the  sun  and  south  stars  gives  for  the  latitude 

41°  35'  35".7  i  0".94 
And  the  mean  of  the  observations  of  Polaris  gives 

410  35/  37».o  1  3".95 

As  these  two  results  differ  from  each  other  by  a  quantity  less  than  their  probable  error,  they  afford 
no  evidence  that  they  are  affected  by  any  constant  errors.  1  have  therefore  taken  as  the  iinal  result 
of  the  observations  their  general  mean,  which  is 

41°  35'  3f>".9  i  0".t>3 

TELEGRAPHIC  DETERMINATION  OF  LONGITUDE. 

The  plan  adopted  for- the  determination  of  the  difference  of  longitude  was  to  allow  the  observers 
at  Washington  and  Des  Moines  to  determine  their  respective  local  times  in  whatever  manner 
was  most  convenient,  and  then  to  compare  these  times  by  means  of  the  electric  telegraph.  For  that 
purpose  it  was  necessary  to  have  the  use  of  the  wires  of  the  Western  Union  Telegraph  Company, 
and  our  thanks  are  due  to  William  Orton,  esq.,  the  president  of  that  company,  for  his  liberality  in 
granting  them  to  us  free  of  all  expense.  We  are  also  under  obligations  to  the  following  named  gen 
tleinen:  to  Mr.  Charles  A.  Tinker,  manager  of  the  Western  Union  lines  in  Washington,  and  to  the 
gentlemen  having  charge  of  the  wires  in  Chicago,  whose  names  I  am  ignorant  of,  for  making  the 
general  arrangements  necessary  to  give  a  continuous  line  of  wire  from  Washington  to  Des  Moines. 


OBSERVATIONS    OF    THK    ECLIPSE    OF    AUGUST    7,    1869.  41 

To  Mr.  M.  Marcan,  chief  operator  in  tin-  Washington  office,  for  coming  up  to  the  observatory  every 
evening  and  assisting'  in  the  management  of  the,  wires  during  the  exchange  of  signals.  To  Mr. 
Monroe  A.  Smith,  manager  of  the  telegraph  otlice  at  Des  MoinevS,  for  assistance  and  facilities  ren- 
dered to  me  there  ;  and  to  the  various  gentlemen,  whose  names  I  do  not  know,  who  had  charge  of 
the  repeaters  at  Philadelphia,  Pittsburg,  C'restline,  Chicago,  Keokuk,  and  Davenport,  during  the 
exchange  of  signals. 

The  signals  employed  in  determining  the  difference  of  longitude  were  made  by  breaking  a  gal- 
vanic circuit ;  a  method  which  1  prefer  because-  the  magnets  used  in  telegraphing  are  much  more 
certain  to  open  promptly  when  the  circuit  is  broken  than  they  are  to  close  promptly  when  it  is 
re-established.  This  is  true  of  a  circuit  including  only  a  single  magnet,  but  it  applies  with  far 
greater  force  when,  as  in  the  present  case,  the  distance  is  so  very  great  that  it  is  necessary  to 
divide  it  into  a  number  of  shorter  circuits  and  to  use  repeaters  to  transmit  the  signals  from  one 
circuit  to  the  other.  The  apparatus  employed  at  the  observatory  in  Washington,  both  for  sending 
and  receiving  signals,  is  entirely  automatic,  and  is  fully  described  in  my  report  on  the  determina- 
tion of  the  longitude  of  the  city  of  Havana,  Cuba.  That  used  at  Des  Moines  consisted  of  a  break 
circuit  key,  which  I  carried  with  me,  and  the  usual  receiving  magnet  and  sounder;  the  armature 
of  I  lie  magnet  of  the  sounder  being  so  adjusted  as  to  make  its  back  stroke  much  louder  than  its  for- 
ward one. 

At  Washington,  the  pendulum  of  the  Kessels  sidereal  clock  broke  the  circuit  for  somewhat  less 
than  one-tenth  of  a  second  every  time  it  passed  the  central  point  of  its  arc;  thus  making  a  break 
once  every  second.  Halfway  between  the  clock  break  corresponding  to  0  seconds  and  that  corre- 
sponding to  1  second,  an  extra  break  was  interpolated  by  means  of  a  key  worked  by  hand;  thus 
marking  the  beginning  of  each  minute  by  a  double  break.  These  signals,  after  passing  through 
the  various  intermediate  repeaters,  finally  arrived  at  lies  Moines  and  were  made  audible  by  the 
sounder  there.  Sitting  beside  it,  and  keeping  my  eye  upon  the  mean-time  chronometer,  I  waited 
until  the  back  stroke  of  the  armature  of  the  sounder  coincided  with  the  beat  of  the  chronometer. 
When  that  occurred  I  noted  the  time;  and  also  the  time  of  the  arrival  of  the  next  following  double 
beat  of  the  Washington  clock.  Five  such  coincidences  were  observed  on  each  night  when  signals 
were  exchanged,  and  at  their  conclusion  the  Washington  operator  told  me  the  hour  and  minute 
corresponding  to  the  last  double  beat  of  his  clock.  The  following  record  of  signals  received  at  Des 
Moines.  from  Washington,  on  the  evening  of  August  7,  1809,  is  given  as  a  specimen  of  such  work  : 

Cdiiicidc-nc;'  of  brcak.s  with  Nuxt  following 

limits  of  chronometer.  double  break. 

It.     in.        «.  ». 

2     30     18.0  01. 0 

33     10.5  00..-, 

30     18.0  00.0 

39     10.5  59.5 

42     18.0  59.0  =  IS"  38'"  Os.O,  Washington  clock. 

Now,  as  the  double  breaks  correspond  to  the  0  seconds  of  the  Washington  clock,  if  we  add  00 
to  the  observed  seconds  of  the  time  of  coincidence  of  beats,  and  then  subtract  from  the  sum  the  sec 
onds  of  the  time  of  the  next  following  double  beat,  the  remainder  will  be  the  seconds  indicated  by 
the  face  of  the  Washington  clock  at  the  time  of  the  coincidence  of  beats.  Thus,  for  the  first  coin- 
cidence recorded  above,  (JO"  +  18s.O  —  01s.O  =  17s.O.  The  last  recorded  coincidence  and  double  beat 
give,  not  only  the  seconds  of  the  Washington  clock,  but  the  hour  and  minute  also;  thus  furnishing 
the  means  of  supplying  the  hour  and  minute  to  each  of  the  other  coincidences.  Proceeding  in  that 
manner  with  the  record  given  above,  we  obtain 

Chronometer.  Washington  clock. 

h.      m.        «.  It.       in.        s. 

2     30     18.0  18     25     17.0 

33     10.5  28     10.0 

30     18.0  31     18.0 

39     10.5  34     17.0 

42     18.0  37  '  19.0 

6* 


42 


REPORT    OF    PROFESSOR   HARKNESS. 


These  are  the  desired  comparisons  of  the  clock  and  chronometer,  obtained  at  DCS  Moines.  In 
order  to  eliminate  the  time  occupied  in  the  transmission  of  the  signals,  it  was  necessary  that  a  .sim- 
ilar set  of  comparisons  should  be  obtained  at  Washington.  For  that  purpose,  as  soon  as  the  com- 
parisons at  Des  Moines  were  finished,  the  otliccr  at  Washington  put  his  clock  out  of  the  main  cir- 
cuit, and  arranged  his  chronograph  so  that  while  it  recorded  the  beats  of  his  clock  it  would  also 
record  along  with  them  the  signals  sent  from  DCS  Moines.  Then,  placing  my  hand  above,  but  not 
in  contact  with,  the  break-circuit  key,  1  beat  seconds  with  my  linger,  in  coincidence  with  the  beats 
of  my  chronometer,  touching  the  key  at  every  beat,  but  only  pressing  it  hard  enough  to  break  tin- 
circuit  at  the  beats  corresponding  to  0,  1,  5,  10,  15,  20,  25,  30,  35,  40,  45,  50,  55,  0,  &c.,  &<•.,  seconds. 
Thus  breaks  were  transmitted  to  Washington,  and  recorded  upon  the  chronograph,  at  regular  inter- 
vals of  five  seconds,  and  the  beginning  of  each  minute  was  marked  by  a  double  break.  Finally, 
after  a  sufficient  number  of  such  signals  had  been  sent,  1  telegraphed  to  Washington  the  hour  and 
minute  indicated  by  my  chronometer  at  the  last  double  break.  The  following  record  of  the  breaks 
received  at  Washington  from  Des  Moines,  read  from  the  chronograph  sheets  of  the  evening  of 
August  7.  1809,  is  inserted  as  a  specimen  of  such  work. 

Each  comparison  consists  of  nine  signals;  namely,  all  those  occurring  at  intervals  of  live  sec- 
onds between  40  seconds  of  one  minute  and  20  seconds  of  the  next  following  minute,  by  the  face  of 
the  chronometer.  As  the  chronograph  has  but  a  single  pen,  by  which  both  the  clock  beats  and  the 
signals  are  recorded,  in  order  to  avoid  inaccuracy  in  reading  off  the  sheets,  no  use  is  made  of  sig- 
nals which  occur  very  iiear  the  time  of  coincidence  of  beats  of  the  clock  and  chronometer.  • 

Chronometer. 


h.      m.        a. 
2     49     0.0 


Washington 

clock. 

Chronometer. 

*.40 

.40 

.50 

A.       m. 

.45 

A.         TO.         9. 

18    44 

2.43 

2     50     0.0 

.40 

.50 

.55 

.50 

\V:isliingioii 

clock. 

Chronometer.          Washington  clock. 

a. 

8. 

.55 

.70 

' 

.60 

.SO 

.(iO 

.85 

li.       m. 

.60 

//.     m.      8.               A.      m.       .80 

18     45 

2.05 

2     51     0.0            18     46     2.SO 

.70 

.88 

.85 

.80 

.70 

.88 

.70 

.90 

Taking  the  means  we  get 


Chronometer. 
li.      m.       s. 
2     49     0.0 

50  0.0 

51  0.0 


Washington  clock. 

/I.          Ml.  K. 

18     44    2.46 

45  2.66 

46  2.82 


which  are  the  desired  comparisons  of  the  clock  and  chronometer,  obtained  at  Washington. 

As  our  temporary  observatory  at  Des  Moines  was  more  than  three-quarters  of  a  mile  from  the 
telegraph  office,  in  order  to  guard  against  the  introduction  of  any  error  into  the  longitude,  by  the 
chronometer  tripping  while  it  was  being  carried  from  one  place  to  the  other,  1  always  compared  it 
with  the  mean-time  chronometer  T.  S.  <S:  J.  I).  Negus  No.  1300,  immediately  before  starting  for  the 
telegraph  office,  and  again  immediately  after  returning  from  it.  1  always  walked  from  one  place 
to  the  other,  and  carried  the  chronometer  in  my  hand,  so  as  to  subject  it  to  as  little  motion  as  pos 
sible. 

The  observations  for  time  at  Washington  are  given  in  full  in  Schedule  (',  appended  to  this  report. 
They  were  made  with  the  east  transit  instrument,  by  Professor  M.  Yarnall,  U.  S.  N.,  who  has  also 
reduced  them  and  furnished  me  with  the  clock  errors  which  I  have  employed.  The  error  of  the 
chronometer  Negus  1319,  on  Des  Moines  mean  time,  during  the  exchange  of  longitude  signals  on 
the  evenings  of  July  26,  29,  30,  and  31,  has  been  obtained  from  the  hourly  rate  and  error  at  noon 
given  for  that  chronometer  on  these  days  respectively  in  the  table  on  page  36.  For  the  evening  of 
August  7  the  error  has  beeu  found  as  follows:  From  July  23  to  August  7  the  time  observations 
show  that  the  chronometer  was  steadily  gaining ;  while  the  observations  of  August  8  show  that 


OBSERVATIONS    OF  THE   ECLIPSE   OF  AUGUST  7,    1869. 


43 


during  the  twenty -four  hours  preceding  tin-  noon  of  tlmt  day  it  lost  two-tenths  of  a  second.  The 
question  arises  whether  the  change  of  rate  took  place  before  or  after  the  exchange  of  longitude 
signals  on  August  7.  To  answer  that  question  we  have  the  following  comparisons  of  chronometers : 


\rj;iis  lliOO.     Negus  1H19. 

1869. 

ft. 

in. 

s. 

ft. 

in. 

8 

August   7 

:« 

6 

0.0 

=  :! 

8 

8 

6 

7 

12 

57 

0.0 

=  12 

59 

8 

7 

7 

16 

8 

0.0 

=  16 

10 

8.7 

8 

6 

38 

II.  0 

=    6 

40 

8 

1 

As  the  longitude  signals  were  exchanged  between  14h  30m  and  luh  Om,  by  the  face  of  Negus 
1319,  these  comparisons  seem  to  indicate  that  the  change  of  rate  took  place  afterwards.  The 
observations  make  Negus  1319 

C1'  18m  17S.3  fast 

at  noon  of  August  7,  and  for  the  preceding  ten  days  it  gained  on  aw  average  0.58  of  a  second  per 
day.  Hence,  its  error  at  the  time  the  signals  were  exchanged  would  be  6h  18m  17S.50.  I  have  pre- 
ferred to  use  a  slightly  less  value,  and  have,  adopted 

G1'  18'"  17".4  fast. 


Throughout  the  following  record  of  the  exchange  of  signals,  the  error  of  the  Kessels  clock  is 
given  on  Washington  sidereal  time,  and  the  error  of  the  chronometer  Negus  1319  on  mean  time  at 
our  temporary  observatory  in  Des  Moincs. 

On  account  of  the  great  distance  between  the  two  cities,  it  was  impossible  to  transmit  tele- 
graphic signals  directly  from  Washington  to  DCS  Moines;  therefore  the  line  was  broken  up  into  a 
number  of  circuits  of  moderate  length,  and  the  signals  transmitted  from  one  circuit  to  the  other  by 
means  of  automatic  repeaters;  the  arrangement  of  which  depended  upon  the  electrical  condition  of 
the  wires,  and  the  exigencies  of  the  business  of  the  telegraph  company,  and  was  varied  from  night 
to  night;  the  particular  arrangement  made  use  of  on  each  night  being  stated  in  the  record  of  that 
night's  work.  The  number  of  statute  miles  of  wire,  exclusive  of  the  wire  in  the  magnets,  the  kind 
of  repeaters,  and  the  amount  of  battery  used  on  each  circuit  that  was  employed,  were  as  follows: 

Washington  to  Philadelphia,  138  miles.  Thirty  drove  cups  at,  Washington.  A  Hix  repeater 
and  thirty  drove  cups  at  Philadelphia. 

I'hilailelphia  to  rittstburg,  355  miles.  A  Hix  repeater  and  fifty  Grove  cups  at  Philadelphia.  A 
Hix  repeater  and  sixty-five  drove  cups  at  Pittsburg. 

Fittxlmrg 1<>  Crcxtliiic,  189  miles.  A  Hix  repeater  and  sixty-five  Grove  cups  at  Pittsburg.  A 
Hix  repeater  and  seventy-five  Grove  cups  at  Crestline. 

Crestline  to  Chicago,  270  miles.  A  Hix  repeater  and  seventy-five  Grove  cups  at  Crestline.  A 
Hix  repeater  and  sixty  Grove  cups  at  Chicago. 

Pittsburg  to  Chicago,  408  miles.  A  Hix  repeater  and  sixty-five  Grove  cups  at  Pittsburg.  A  Hix 
repeater  and  sixty  Grove  cups  at  Chicago. 

Chicago  to  KcoJmk,  251  miles.  A  Hix  repeater  and  sixty  Grove  cups  at  Chicago.  A  button 
repeater  and  two  hundred  and  fifty  cups  of  Hill's  battery  at  Keokuk. 

Keoltulc  to  Des  Moines,  101  miles.  A  button  repeater  and  two  hundred  and  fifty  cups  of  Hill's 
battery  at  Keokuk.  Ninety  cups  of  Hill's  battery  at  Des  Moines. 

Chicago  to  Davenport,  183  miles.  A  Hix  repeater  and  sixty  Grove  cups  at  Chicago.  A  button 
repeater  and  sixty-five  Grove  cups  at  Davenport. 

Davenport  to  Des  Moines,  174  miles.  A  button  repeater  and  sixty-five  Grove  cups  aj  Daven- 
port. Ninety  cups  of  Hill's  battery  at  Des  Moines. 

Hill's  battery  is  a  modification  of  Darnell's,  each  cup  consisting  of  a  glass  jar,  about  seven 


44  REPORT    OF    PROFESSOR    HARKNESS. 

inches  high  and  six  inches  in  diameter,  with  a  sheet  of  copper  placed  in  the  bottom,  and  a  disk  of 
zinc,  perforated  in  the  center,  suspended  horizontally  about  five  and  a  half  inches  above  the  copper. 
Each  of  these  plates  has  a  surface  of  about  twenty-eight  square  inches,  and  has  attached  to  it  a 
gutta-percha  covered  copper  wire,  which  forms  one  pole,  of  the  battery.  The  jar  is  tilled  with  a  solu- 
tion of  sulphate  of  zinc,  after  which  a  few  crystals  of  sulphate  of  copper  are  dropped  in  through  the 
orifice  in  the  /inc,  and  lie  on  the  copper  plate.  If  the  liquid  is  not  agitated  the  copper  plate  will 
lie  in  a  solution  of  sulphate  of  copper,  and  the  zinc  plate  in  a  solution  of  sulphate  of  zinc,  so  long  as 
the  specific  gravity  of  the  latter  is  less  than  36°  li.  The  porous  cell,  used  in  Daniell's  battery,  is 
therefore  dispensed  with.  For  telegraphic  purposes  seventy  cups  of  Hill's  battery  are  considered 
equal  to  forty-three  cups  of  Grove. 

The  difference  between  a  Hix  and  button  repeater  is,  that,  when  a  llix  repeater  is  properly 
adjusted,  signals  can  be  sent  through  it  with  equal  facility  in  either  direction  ;  while  if  signals  are 
being  sent  through  a  button  repeater  in  one  direction,  before  they  can  be  sent  in  the  opposite  direc- 
tion an  attendant  must  change  the  connections  of  the  wires.  This  is  done  by  means  of  a  switch,  or 
button  ;  hence  the  name,  "  button  repeater."  In  the  case  of  all  repeaters,  signals  going  in  one  direc- 
tion pass  through  a  different  set  of  magnets  from  those  going  in  the  opposite  direction;  therefore 
there  never  can  be  any  security  that  in  any  given  case  the  signals  going  in  opposite  directions  occu- 
pied the  same,  length  of  time  in  their  transit;  however,  as  the  repeaters  will  only  work  within  very 
narrow  limits  of  adjustment,  aiwl  as  the,  combined  wave  and  armature  time  varies  so  little  on  different 
nights,  the  error  originating  from  this  source  must  be  exceedingly  small,  and  in  the  mean  of  five 
nights  it  is  probably  entirely  eliminated. 

The  total  length  of  wire,  exclusive  of  that  on  the  magnets,  between  Washington  and  Des 
Moines,  via  Keokuk,  is  1,373  miles ;  and  via  Davenport,  1,318  miles. 

KKCOKD    OF   EXCHANGE   OF   SIGNALS. 

July  21  i,  1800. — Uepeaters  at  Philadelphia,  Pittsburg,  Crestline,  Chicago,  and  Keokuk. 
Comparison  of  chronometers  to  show  whether  or  not  Negns  1319  suffered  any  appreciable  change 
in  its  error  while  being  carried  to  the  telegraph  office  and  back  : 

Negn«  1300.  Negus  131!'. 

li.       m.       s.  /i.        m.        x. 

11     22    0.0  11     24     7.8 

5     47     0.0  5    49     8.0 

Kessels  clock,  22s. 45  fast. 

Chronometer  Negus  1310,  G1'  18"'  9S.S  fast. 

Comparisons  of  clock  and  chronometer  by  means  of  signals  received  at  Des  Moines: 

Negus  1319.  Kessels. 

/I.        III.  #.  ll.        III.  H. 

3  57     55.5  19     5    53.0 

4  0    50.0  8     48.0 
52     50.5                    20     0    57.0 
55     41.0                            3     48.0 

4  58    50.5  G    58.0 

5  1     52.0  10       0.0 

Reducing  all  these  comparisons  to  the  same  instant,  we  get 

Negns  1319.  Kessels. 

ft.      m.        K.  li.      m.      *. 

3     52    3.47  10    0     0.0 

3.44 

3.49 

3.45 

3.47 

3.47 


OBSERVATIONS    OF    THE    ECLIPSE    OF   AUGUST   7,    1869.  45 

Taking  the  mean,  applying  the  clock  and  chronometer  errors,  and  reducing  the  Washington 

sidereal  time  to  tlic  corresponding  mean  time,  there  results 

Wasliiii-itnn.  Des  Moiiics.  Dift'.  longitude. 

.10"  40'"  !»s.r,.-)  9"  .33™  5.T.60  1"  6'"  15S.89 

Comparisons  of  clock  and  chronometer  by  means  of  signals  received  at  Washington: 

NCfJUS  liil'.l.  Krssrls. 

/I.         III.  «.  /I.  III.  0. 

4     10    0.0  lit     17     59.87 

12     0.0  liO       0.21 

i:i     0.0  21       0.38 

Reducing  all  these  comparisons  to  the  same  instant,  we  get 

Nl'gll.s  KU',1.  Krssrls. 

7i.      in.        ».  /i.        111.          i. 

4    10    o.o  10    17    r>9.87 

39.88 

59.89 

Taking  the  mean,  applying  the  clock  and  chronometer  errors,  and  reducing  the  Washington 
sidereal  time  to  the  corresponding,  mean  time,  there  results 

\V:ishini;toii.  Des  Moines.  "Dill',  longitiulp. 

10"  58"  Cr.lS  9"  51'»  50».20  I'1  6'"  1G".2S 

The  difference  of  longitude  found  from  the  signals  received  at  Washington  necessarily  varies 
from  that  found  from  the  signals  received  at  1  )es  Moines.  The  mean  of  the  two  results  is  lh  0'"  l(is.OS, 
which  is  the  true  dilferenee  of  longitude  given  by  this  evening's  work.  Half  the  difference  between 
the  two  results  is  0.20  of  a  second,  which  is  the  time  occupied  in  the  passage  of  a  signal  from  one 
city  to  the  other.  As  repeaters  were  included  in  the  circuit,  this  is  the  combined  effect  of  wave  and 
armature  time,  and  gives  no  clue  to  the  speed  of  the  galvanic,  current. 

</nltl  29,  1809. — Itepeatcrs  at  Philadelphia,  1'ittsbnrg,  Chicago,  and  Keoknk. 

Comparison  of  chronometers : 

Negus  1300.  Negns  1319. 

/i.       m.        «.  li.       m. 

10     14    0.0  10     1C     8.2 

4     14     0.0  4     16     8.4 

Kessels  clock,  20V>::  fast. 

Chronometer  Negus  1319,  6h  18™  12s.l  fast. 

Comparisons  of  clock  and  chronometer  by  means  of  signals  received  at  Des  Moines: 

Negus  1319.  K.-ssels. 

ft.      m.        s.  It.       m.       8. 

2    45  10.0  18    4  41.0 

48  5.5  7  37.0 

51  15.0  10  47.0 

54  14.5  13  47.0 

57  13.0  10  46.0 

Reducing  all  these  comparisons  to  the  same  instant,  we  get 

Negns  1319.  Kesscls. 

/I.         111.  *.  •  A.         71).          S. 

2  40  29.77         18  0  0.0 
29.75 
29.76 
29.74 
29.75 


46  REPORT   OF   PROFESSOR    IIARKNESS. 

Taking  the  mean,  applying  the  clock  and  chronometer  errors,  and   reducing  the  Washington 
sidereal  time  to  the  corresponding  mean  time,  there  results 

Washington.  Des  Moincs.  J>ilV.  longitude. 

ii'1  2s»'  33s.75  s1-  22-"  i7s.or>  i1'  6»-  i5s.<»± 

Comparisons  of  clock  and  chronometer  by  means  of  signals  received  a)  Washington: 


Negus  1319. 
h.      m.       s.  Ii.       m.          s. 

3     17     0.0  18    36    36.60 

18  0.0  :;7    36.74 

19  0.0  38    36.89 

Reducing  all  these  comparisons  to  the  same  instant,  we  get 

Negus  1319.  Kessds. 

7i.     MI.        s.  h.       m.          n. 

3     17     0.0  18    36    36.60 

36.58 

36.56 

Taking  the  mean,  applying  the  clock  and  chronometer  errors,  and  reducing  the  Washington 
sidereal  time  to  the  corresponding  mean  time,  there  results 

Washington.  Des  Moines.  Diff.  longitude. 

101'  5'"  4s.  15  8"  58     47«.90  1"  (i1"   .16S.25. 

This  evening's  work,  therefore,  gives 

/I.       III.  8. 

Difference  of  longitude  1     t!     lii.O'.l 

Wave  and  armature  time  0     0       0.16 

July  30,  1869. — Repeaters  at  Philadelphia,  Pittsburg,  Crestline,  Chicago,  and  Keokuk. 
Comparison  of  chronometers : 

Xegus  K!00.  Negus  131 !». 

/I.          III.  t>.  ll.  III.  K. 

11    21    0.0  11    23    s.s 

5     36     0.0  5     38     9.0 

Kessels  clock,  21".20  fast  at  the  time  of  the  Des  Moines  comparison  ;  L'l',17  fast  at  the  time  of 
the  Washington  comparison. 

Chronometer  Negus  1319,  C1'  18m  12B.7  fast  at  the  time  of  the,  Des  Moincs  comparison  ;  61'  IS»> 
12S.8  fast  at  the  time  of  the  Washington  coni])arison. 

Comparisons  of  clock  and  chronometer  by  means  of  signals  received  at  Des  Moines: 

Negus  1319.  Kessels. 

7i.      m.  s.  Ii.       HI.        *. 

3    47  3.5  19     10  41.0 

50  5.0  13  43.0 

53  7.5  16  46.0 

56  5.0  19  44.0 

59  6.5  22  46.0 

Reducing  all  these  comparisons  to  the  same  instant,  we  get 

Negus  1319.  Kessels. 

h.     m.         *.  Ji.      m.     s. 

3    36    24.25  19    0    0.0 

24.25 

24.25 

24.23 

24.23 


OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST   7,    1869.  47 

Taking  the  iiu'iin,  applying  the  cluck  and  chronometer  errors,  and  reducing  the  Washington 
sidereal  time  to  the  corresponding  mean  time,  there,  results 

\Yii»liin<rloii.  Jlcs  Muincs.  Dili'.  linifjil  mlr. 

Ill1'  21'"  27MO  <Jh  18'"   11  ".51  I1'  <>'"   15».G2. 

Comparisons  of  clock  and  chronometer  h.y  means  of  signals  received  at  Washington: 

Nri;iis  I'.ili).  Keswels. 

It.     m.      s.  »A.        nt,         ,s. 

5     3     0.0  20     'M     50.20 

4  0.0  27     50.42 

5  0.0  28     50.57 

Reducing  all  thesv  comparisons  to  the  same  instant.  \ve  get 

Nf<;iis  KS19.  Krssrls. 

/'.     lit.       .v.  /*.       in.          x. 

5    ;{    o.o  i'o    liii    ."lO.^'ii 

.-.0.2G 
50.24 

Taking  the  mean,  applying  the  clock  and  chronometer  errors,  and  reducing  the  Washington 
sidereal  time  to  the  corresponding  mean  time,  there  results 

\Viisliin<r|<>ii.  DCS  MoineH.  Hill',  longitude. 

11"  51'"  3».21  10"  44'"  47K.2()  1"  0"'  Ki'-.Ol. 

This  evening's  work,  therefore,  gives 

h.   '  m.        s. 

Difference  of  longitude  1    <i    15.82 

Wave  and  armature  time  '    ()'  0       0.20 

.lull/  :>1,  lS(i!».  —  Kcpcaters  at  I'liiladelphia,  I'ittsburg,  Crestline,  Chicago,  and  Keokuk. 
Comparison  of  chronometers: 


N.-MIIS  1300. 
//.       in.       s. 
1  1      3     0.0 
5     9     0.0 

Negus  i:;i'.i. 
A.      m.       x. 

11     5     8.9 
5  11     9.0 

Kesscls  clock,  L'1\S:;  f;ist. 

ChroiKuneter  Negus  l.'5H»,  (ih  IS"'  liKS  fast. 

Comparisons  of  clock  and  chronometer  by  means  of  signals  received  at  Des  Moines: 


Negus  1319. 

Kessds. 

/I.       »!.           ». 

It.      m.        8. 

4    2     17.5 

19     29     51.0 

5     15.0 

32    52.0 

8     17.5 

35     5.5.0 

23    20.0 

51        0.0 

20     17.5  53     58.0 

Reducing  nil  ihesc  comparisons  to  the  same  instant,  we  get 


Kcssels. 

A.      IH.         n.  li.     m.       8. 

•  '<     32     28.40  1!)     0     0.0 

28.38 

28.38 

28.36 

28.34 


Taking  the  mean,  applying  the  clock  and  chronometer  errors,  and  reducing  the  Washington 
sidereal  time  to  the  corresponding  mean  time,  there  results 

\V;iKliins-|iiii.  DCS  M,  lines.  I  (ill',  longitude. 

10"  20"'  30».<;:;  9"  14'"  148.57  I1'  «»•  lu9.OG. 


48  REPORT   OF   PROFESSOR    HARKNESS. 

Comparisons  of  clock  and  chronometer  by  means  of  signals  received  al  Washington  : 

Negus  1319.  Kessrls. 

/i.      m.       s.  li.      m.         x. 

4    20    0.0  19     57     41. -44 

31  0.0  58     41.58 

32  0.0  5!)     41.74 

Reducing  all  these  comparisons  to  the  same  instant,  we  gel 

Negus  1319.  Kessels. 

/I.       m.         s,  H.        tn.          x. 

4     30     0.0  1!)     57     41.44 

41.42 
41.41 

Taking  the  mean,  applying  the  clock  and  chronometer  errors,  and  reducing  the  Washington 
sidereal  time  to  the  corresponding  mean  time,  there  residts 

Wellington.  Dew  Moines.  I  (ill.  longitude. 

11"  18m  2".«0  10'1  Jl»>  408.20  I1'  0'"   JIJ-.40. 

This  evening's  work,  therefore,  gives 

/I.         III.  X. 

Difference  of  longitude  1     <;    i<>.23 

Wave  and  armature  time  0     n       0.17 

August  7,  180!).— Repeaters  at  Philadelphia,  Pittslmrg,  Chicago,  and  Davenport. 
Comparison  of  chronometers : 

Negus  1300.  NYgiis  1319. 

h.       m.        x.  h.       in.  H. 

12     57     0.0  12    59       8.7 

4       8     0.0  4     10       8.7 

Kessels  clock,  27M(5  fast. 
(Chronometer  Negns  1319,  6h  18'"  17".4  fast. 
Comparisons  of  clock  and  chronometer  by  means  of  signals  received  at  Des  Moines : 

Negus  1319.  Kcsscls. 

/i.      m.  «.  /i.       m.          «. 

2     30  l.S.O  18     25  17.0 

33  10.5  28  10.0 

3G  18.0  31  18.0 

39  16.5  34  17.0 

42  18.0  37  19.0 

Reducing  all  these  comparisons  to  the  same  instant,  we  gel 

N.-gUS  1319.  hYssrls. 

/I.       HI.  S.  /I.         HI.  H. 

3     4    55.31  19    0      o.O 

55.30 
55.30 
55.30 

55.28 

Taking  the  mean,  applying  the  clock  and  chronometer  errors,  and  reducing  the  Washington 
sidereal  time  to  the  corresponding  mean  time,  there  results 

Washington.  Des  Moines.  Mitt',  longitude. 

9h  52"'  538.94  8h  40m  378.90  I1'  li'"   1<;».04. 

Comparisons  of  clock  and  chronometer  by  means  of  signals  received  at  Washington  : 


OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST   7,    18fi9. 


49 


Negus  1319. 
It.      iw.       s. 

2.    49    0.0 

r.o   o.o 

51    0.0 


Kessels. 
li.      m.        «. 
18    44    2.46 

45  2.66 

46  2.82 


I  {oil  iiciiig-  all  these  comparisons  to  the  same  instant,  we  get 

Negus  1319.  Kessels. 

/I.         711.  *.  /I.          'III.  S. 

2    49    0.0  IS    44    2.46 

2.50 
2.49 

Taking  the  mean,  applying'  the  clock  and  chronometer  errors,  and  reducing'  the  Washington 
sidereal  lime  to  the  corresponding  mean  time,  there  results 

\V:ishinn'l<>ii.  lies  Moines.  Dill',  longitude. 

9h  36'"  598.04  S1'  :!0'»  42".GO  1"  61"  169.44. 

This  evening's  work,  therefore,  gives 


li.    m. 


Difference  of  longitude     - 
Wave  and  armature  time 

KexuU  from  the  exchange  of  signals. 
Collecting  the  results  obtained  from  the  different  nights'  work,  \ve  have 


ti 
0 


16.24 
0.20 


\Vavc  :in<l 

Date. 

Diff.  longitude. 

armature 

time. 

1869, 

It.    III.          K. 

X. 

July    26 

1     (i     If,.  08 

0.20 

89 

1C.  09 

.  ii; 

:to 

15.82 

.'JO 

31 

10.23 

.17 

Aug.      7 

16.  24 

0.20 

Taking  tlie  mean,  we  find  that  our  temporary  observatory  at  Des  Moines  was 

I1'  6"'  16S.09  ±  Qs.OS  west 

ot  the  east  transit  instrument  of  the  United  States  Naval  Observatory  at  Washington.  But  the 
east  transit  instrument  is  42.9  feet,  which  in  this  latitude  is  equal  to  0.036  of  a  second  of  time,  to 
the  east  of  the  center  of  the  dome.  Hence  we,  have  as  the  result  of  these  signals  that  the  tempo- 
rary observatory  at  Des  Moincs  was 

I1'  G1"  16S.05  ±  0-s.05  west 

of  the  center  of  the  dome  of  the  United  States  Naval  Observatory  at  Washington.  From  a  series 
of  observations  made  since  my  return  to  Washington,  I  have  satisfied  myself  that  if  any  personal 
equation  exists  between  Professor  Yarnall's  determination  of  the  time  with  the  east  transit  instru- 
ment and  my  determination  with  the  sextant,  it  is  so  small  as  to  be  entirely  hidden  by  the  acci- 
dental errors  inseparable  from  sextant  observations. 

TEIANGULATION  CONNECTING  THE  VARIOUS  TEMPORARY  OBSERVATORIES. 

« 

In  order  to  ascertain  the  relative  positions  of  the  temporary  observatories  of  the  different 
astronomers  who  might  be  at  Des  Moines,  1  took  with  me  several  small  pocket  surveying  instru- 
ments, which  were  the  best  at  my  command.  Subsequently  Colonel  J.  W.  Otley,  engineer  of  the 
Des  Moines  Valley  railroad,  kindly  lent  me  a  small  theodolite,  which  was  much  better  adapted  to 
the  accomplishment  of  my  purpose,  and  with  which,  in  connection  with  Dr.  C.  H.  F.  Peters,  I  exe- 
cuted the  triangulatipn  shown  in  Plate  III.  The  theodolite  was  made  by  Spears  &  Co.,  of  Dublin, 
and  was  of  the  English  pattern,  the  range  of  the  telescope  being  limited  to  altitudes  not  much 
greater  than  sixfy  degrees.  Its  horizontal  and  vertical  limbs  were  each  five  inches  in  diameter, 


50 


EEPOET   OF   PROFESSOR    IIARKNESS. 


divided  to  thirty  minutes,  and  read,  the  horizontal  limb  by  two  verniers,  the  vertical  limb  by  one 
vernier,  to  single  minutes.  The  telescope  had  a  focal  length  of  nine  and  one-quarter  inches,  a  clear 
aperture  of  one  inch,  and  a  magnifying  power  of  thirty  diameters. 

The  base-line  was  situated  upon  a  low  level  island  in  the  DCS  Moines  Uiver,  to  the  east  of  our 
observatory,  and,  from  two  very  careful  measurements  made  with  the  Chesterman  metallic  tape,  was 
found  to  be  l,0.'>l)..')fcet=314.72  meters*  in  length.  The  signals  North  IJase,  South  P.ase,  Kast  Signal, 
and  West  Signal,  were  Hags  attached  to  small  poles  eight  or  ten  feet  high.  The  signal  "Naval 
Observatory  "  was  the  south  peak  of  the  roof  of  our  temporary  observatory.  The  signal  "  Litchfield 
Observatory"  was  a  Hag  placed  on  the  east  side  of  the  temporary  observatory  occupied  by  Dr.  ('. 
H.  P.  Peters  and  party.  The  signal  "Court-house"  was  the  center  of  the  dome  of  the  ( 'onrt  house. 
Near  it  Professor  Simon  Newcomb,  United  States  Navy,  and  Professor  ,1.  K.  llilgard,  United  Stales 
Coast  Survey,  with  their  parties,  observed. 

In  almost  all  cases  the  angles  between  the  different  signals  were  measured  both  by  Dr.  Peters 
and  myself,  each  of  us  repeating  the  angle  six  times.  The  results  are  given  in  the  following  table — 
the  column  headed  "II"  containing  my  measures, that  headed  "P"  Dr.  Peters's  measures,  and  that 
headed  "concluded"  the  concluded  value  of  the  angle,  which  is  generally  the  mean  of  the  results 
contained  in  the  columns  "  II"  and  "  P."  In  the  case  of  the  angles  at  West  Signal  I  have  rejected 
Dr.  Peters's  measures  because  they  were  made  a  day  later  than  mine,  and  I  am  almost  certain  that 
during  the  interval  some  of  the  signals  were  disturbed  by  cattle: 

Alixlwt  of  (Hwrrnl  AiKjlrx. 


Date. 

Station. 

Object. 

X  umber  of 
repetitions. 

Observed  angle. 

H. 

P. 

Concluded. 

1869. 
Aug.  3 

East  Signal 

Court-house  and,Sonth  Base    . 

6 

i       n 
65  27  CO.tl 

53.  :\ 

56.6 

Coort-boiiBe  and  West  Signal  .     .     . 

« 

68  32  36.  2 

30.5 

33.  4 

South  Base  and  North  Base     .... 

r> 

40  38  22.  5 

34.2 

28.4 

West  Signal  and  Naval  Observatory 

r, 

2  20    0.  0 

41.7 

20.8 

Litchfield  Observatory  and  Court-house 

r. 

67  49    2.5 

2.5 

2.5 

Litchn'eld  <  Misei  valory 

Court-house  and  Weat  Signal 

(i 

69  44  25.  0 

19.2 

22.  It 

Xnrtli  I'.ase 

Court-house  and  Litchlield  Oliservatory 
Kast  Si(rn;tl  ;i]id  South  Base 

1 

6 

<; 

2  28 
55  10  17.5 

:;t  yti  55.0 

36.6 

63.3 

96.  a 

59.  •> 

South  Base  and  West  Signal   .... 

South  Base  and  Naval  Observatory   .      - 

6 

II  :,->  19.2 

10.8 

15.11 

South  Base 

North  Base  and  Kast  Signal     .... 

(i 

84  11   I'.l.? 

1.7 

11).  7 

West  Signal  and  North  Base    .... 

r> 

86     4  f,(l.  II 

5-.'.  5 

56.2 

Kast  Signal  and  Court-house  .... 

6 

97  33  42.  5 

56.  0 

49.2 

West  Signal  and  Naval  Observatory 

6 

3  22  40.  0 

43.  3 

41.6 

Wrst  signal 

North  Base  and  South  Base     .... 

(i 

<;•->  34  50.6 

511.0 

4 

North  Base  and  South  liasc     .... 

6 

62  34 

20.8 

3 

North  Base  and  East  Signal    -      -      -.    - 

r> 

55  56  34.2 

34.2 

4 

Xorth  Bane  and  East  Signal    .... 

6 

55  56 

11.7 

3 

Kast  Signal  and  Court-house  .... 

« 

86    2  57.5 

51.  2 

4 

Kast  Signal  and  Court-house  .... 

6 

86    2  45.  0 

108.3 

Litchlield  Observatory  and  Court-house 

C> 

74  47  43.3 

%.  7 

I:1,.  :: 

Court-house  and  Naval  Observatory 

1 

110  20 

Naval  Ohscr\atory  and  North  I'.ase  .      . 

1 

107  35 

*  I  have  taken  1  meter  at  32"  Kahr.  ==3<».3(>f5  inehes  at  62"  Fahr. 

tThe  theodolite  could  not  be  placed  in  the  position  occupied  by  the  signal  "  Lilclilicld  Observatory,"  and  therefore 
it  was  jilaeed  eccentrically  at  a  distance  of  5s. (Mi  l'eet=  17.70  meters.  The  reduction  to  the  center,  computed  ill  the 

usual  manner,  is  1°  17'  4".2,  to  be  added  to  the  angle  given  in  the  table.  Hence.  Hie  tr bserved  value  of  the  angle 

between  Court-house  and  West  Signal  is  7.1"  1'  26".3. 


OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST    7,    1869. 


51 


Converting  these  observed  angles  into  observed  directions,  we  yet  the  numbers  given  in  the 
third  column  of  the  following  table  : 

Table  of  Observed  and  Adjusted  Directions. 


Station. 

Object. 

Observed 
direction. 

Correc'n  by 
adjustment. 

Adjusted 
direction. 

o       '      // 

// 

0         '          II 

East  Signal   .... 

Litehlield  Observatory  .      . 

o   o   o.n 

-    7.5 

359  59  52.  5 

Court-house    

67  49    2.5 

—    3.2 

67  48  59.  3 

Smith  Base      

133  16  59.1 

-    2.6 

133  16  56.  5 

\\Ysl   Signal            .      , 

136  21  :i5.9 

+  21.6 

136  21  57.  5 

Naval  Observatory  . 

138  41  56.  7 

+  13.2 

138  42    9.  9 

North  Base      

I"!  55  27.5 

-  15.8 

173  55  11.7 

Litehtield  Observatory 

Court-house    

(I     0    0.0 

-  22.6 

359  59  37.  4 

West  Signal    

71     1  36.3 

+  22.6 

71     1  48.9 

North  Base    .... 

Kasl  Signal      
South  Base 

0     0     0.  0 
55  10  26.2 

+  14.0 

+     8.0 

0     0  14.0 
55  10  34.2 

West  Signal     

86  31  25.  4 

-  22.0 

86  31    3.  4 

South  BMM-    .... 

Naval  Observatory    . 
\orlh  Base 

100    a  41.2 
0     0    0.  0 

-    2.5 
—    5.6 

100     2  38.7 
:!59  59  54.  4 

East  Signal 

*4  11   16.7 

+    2.3 

84  11  19.0 

Court-house    

181  45     5.9 

+     8.  5 

HI   45  14.4 

\\Yst  Signal    

27:!  55    3.8 

-     5.2 

273  54  5S.ll 

\VeM  Signal  . 

\a\al  Observatory    -      .      . 
Nortli  Base 

277  17   15.  1 

0     0     0.0 

+     1-4 
+  19.6 

277  17  46.8 
0     0  19.  6 

Kasl  Signal     

55  5«i  :;!.•„> 

-  18.2 

55  56  16.  0 

Soulli  Base      

62  34  50.  0 

+     4.6 

62  34  54.  6 

Lituhlield  Observatory  .      . 

07  11  42.1 

+     1.9 

67  11  44.0 

Court-house    

111  51)  25.4 

—    5.8 

141  59  19.6 

Naval  Observatory   .      .      . 

252  25  25.  0 

—    2.0 

252  25  23.  0 

1  n  order  to  facilitate  the  adjustment  of  this  triangulation  by  the,  method  of  least  squares,  I  have 
adopted  the  following  notation  : 

1=  North  Base. 

2  =  South  Base. 

3  =  East  Signal. 


5  =  Naval  Observatory. 

(>==<Conrt-house. 

7  =  Litchfield  Observatory. 


4  =  West  Signal. 

1  2  :>  would,  therefore,  denote  the  angle  North  Base,  South  Base,  East  Signal ;  (£)  woidd  denote 
the  direction  from  South  Base  to  North  Base;  and  (:|)  would  denote  the  direction  from  South  Base 
to  East  Signal.  Hence  ( — 2  +  2)  would  denote  the  angle  123. 

Proceeding  in  the  usual  manner,*  the  quadrilateral  1324  furnishes  the  side  equation 

sin  142. .sin  123.  sin  134=sin  124.  sin  132.  sin  143. 
and  the  three  angle  equations 

1800  =  132  +  321  +  213 
1800  =  124  +  241  +  412 
1800  =  134  +  341  +  413 

from  which  we,  derive  the  equations  of  condition 

0=  +    29.6  +  0.4(1)  +  ;,.!  (j)_(U(i)  +  0.2  (>)  —  2.8(J)  +  0.3  (•)  +  0.2  (4)  +  2..1  (jj)  -  1.5  (•<)  I. 

0=+    11.3-  (j)  +  (J)_(i)  +  (|)  -(?)  +  (?)  II. 

0=  + 111.2  — («)  +  (J)-(J) +  (>)_(»)  +  («)  jv. 


1  See  a  paper  by  Charles  A.  Schott,  csq.,  in  the  United  States  Coast  Survey  Report  for  1854,  page  80*  vt  xcq. 


52 


REPORT   OF   PROFESSOR    HARKNESS. 


The  quadrilateral  2346  furnishes  the  side  equation 

sin  632.  sin  462.  sin  342  =  sin  263.  sin  246.  sin  234. 
from  which  we  derive  the  equation  of  condition 
0= +137.7  —  7.9(g)  +  47.1(i)  +  32.8(5)  — 14.7(«)  +  21.2(!>)  —  14.:{(j)  — 18.1(5)  —  6.0(:!)  —  3!).-'(J)    V. 

These  five  equations  of  condition  give  rise  to  the  following 

Equations  of  correlatirfx. 


V 

oiKi 

o-iKj 

o3K3 

0& 

«5K5 

(?) 

+  1 

-I 

(?) 

-  1 

1 

(1) 

+  1 

+  1 

(1) 

—  0.4 

-  1 

+  1 

(I) 

+  0.2 

+  1 

—    6.9 

«) 

+  0.2 

-  1 

—  14.3 

(i) 

+  21.2 

cj) 

+  o.:i 

+  1 

+  1 

CD 

+  2.5 

-  1 

+  47.  1 

(i) 

—  2.8 

-  1 

—  39.2 

(i) 

-    7.9 

(3) 

+  11.4 

-  1 

-  1 

(!) 

+  1.1 

+  1 

+  :«.8 

(I) 

—  1.5 

+  1 

-  18.1 

(5) 

-  11.7 

K4  =  — 20.2 
K5=  +    0.31)9 


The  resulting  normal  equations  are 

0=+  '29.6+    18.04  K, 

+    11.3-      1.60       +    6.00  K2 

+    45.4+      0.10          -   2.00       +    6.00  K3 

+ 111.2  +      1.20       +    2.00       +    2.00       +    6.00  K4 

+  137.7  +  286.50        -54.00       +47.10       +21.10       +  6138.54  K5 

Solving,  we  find 

K,=:— 6.08 
K2=  +  6.20 
K:i=  -1.81 

Substituting  these  values  in  the  equations  of  correlatives,  we,  obtain  the  corrections  to  the 
observed  directions  given  in  the  column  "Correction  by  adjustment"  of  the  table  of  observed  and 
adjusted  directions. 

The  quadrilateral  1  325  furnishes  the  side  equation 

sin  315.  sin  235.  sin  521  =  sin  531.  sin  r>23.  sin  215 
from  which  we  derive  the  equation  of  condition 

0=  — 324.5  — 2.5 (I)  +  25.2 (»)  —  9.3  (:;)  VI. 

The  quadrilateral  3245  furnishes  the  side  equation 

sin  235.  sin  425.  sin  543  =  sin  523.  sin  542.  sin  435 
from  which  we  derive  the  equation  of  condition 

0=  + 342.4  —  29.7  (g)  +  26.7  (=)  —  5.0  (J) 


OBSERVATIONS    OF    THE    ECLIPSE    OP    AUGUST    7,    1369. 
The  equations  of  conditions  VI.  and  VI J.  give  rise  to  the  following 

Equations  of  correlatives. 


53 


V 

a,K, 

«& 

(f) 

—    2.5 

(I) 

-    9.3 

+  26.  7 

(3) 

+  25.2 

-  29.7 

(S) 

-    5.0 

The  resulting  normal  (-([nations  are 


=  — 324.5  +  727.8  K, 

+  342.4  —  996.8       +  1020.0  K, 


Solving,  we  lind 


K,  =  +  0.994 


K2  =  +  0.400 


Substituting  these  values  in  the  equations  of  correlatives,  we  obtain  the  corrections  to  the 
observed  directions  given  in  the  column  "Correction  by  adjustment"  of  the  table  of  observed  and 
adjusted  directions. 

The  quadrilateral  .'3407  furnishes  the  side  ('([nation 

sin  340.  sin  730.  sin  074  =  sin  034.  sin  073.  sin  740 
from  which  we  derive  the  equation  of  condition 

()=  -57.3-0.4(5)-  1.11  («)  +  1.2(<)  f  0.1  (I)  VIII. 

The  equation  of  correlative  is: 


The  normal  equation  is 
Solving,  we  Hud 


0=  —57.3  +  3.05  K, 
K,    =+18.8 


Substituting  this  value  in  the  equation  of  correlative,  we  obtain  the  corrections  to  the  observed 
directions  given  in  the  column  "Correction  by  adjustment"  of  the  table  of  observed  and  adjusted 
directions, 

Applying  the  "Corrections  by  adjustment"  to  the  observed  directions,  we  obtain  the  adjusted 
directions,  by  means  of  which  the  whole  triangulation  has  been  computed,  as  follows — the  lengths 
of  the  sides  being  given  in  meters : 


54 


REPORT   OF   PROFESSOR    HARKNESS. 


No. 

Deuomiuation. 

Observed 
angles. 

Corr.  by 
adjust. 

Planr  angles 
anil  ilislauiT'S. 

Logarithms. 

North  Base  —  South  Rase 

o      /      // 

// 

31  1.72 

2.  497923 

I. 

East  Signal     '.     . 
North  Base     
South  Base      
East  Signal  —  South  Base    
East  Signal  —  North  Base    ... 

40  38  28.4 
55  10  26.2 
84  11  16.7 

13.2 
6.0 
+      7.9 

40  38  15.2 
55  10  20.2 
-1   11  24.6 
306.66 
480.76 

0.  1*623* 
11.  1114276 
9.99776:1, 
2.  598437 
2.  681924 

314  72 

2.  497923 

II. 

West  Signal    
North  Base     
South  Base     

62  34  50.  0 
31  20  59.  2 
86    4  56.2 

15.0 

—     30.11 
0.4 

62  34  35.0 
31  20  29.  2 

86    4  55.8 
1*4  42 

0.  051770 
9.71611* 

9.  998984 
2  265811 

, 

353.  73 

2.  548677 

III. 

East  Signal  —  South  Base  
West  Signal  .  .  .  
East  Signal  
South  Base  
West  Signal  —  South  Base  
West  Signal  —  East  Signal  

6  38  15.8 
3    4  36.8 
170  16  12.  it 

+     22.  8 
+    24.2 

+       7.5 

3116.  6* 
6  38  38.  6 
3     5     1.0 
170  16  20.4 
184.43 
579.  29 

2.59*137 
0.  936663 
8.  730727 
9.387798 
2.  26,'i*-:7 
2.762898 

West  Signal—  North  Base  .  . 

353.  73 

2.  548677 

IV. 

East  Signal  
West  Signal  -  , 
North  Base  
East  Signal  —  North  Base 

37  33  51.  6 
55  56  34.2 
86  31  25.  4 

-     37.4 

-     37.  H 
-     3(5.0 

37  33  14.2 
55  55  56.  4 

.-d  :;o  in.  i 
1-0.76 

0.  215021 
9.  918228 
9.999196 
2.  681926 

East  Signal  —  West  Signal 

579.  29 

2.  762894 

East  Signal  —  West  Signal 

579.  29 

2.  762896 

V. 

Court-house    
East  Signal     • 
West  Signal    
Court-house  —  West  Signal  
Court-house  —  East.  Signal 

68  32  33.  1 
*<>    2  51.2 

+     21.* 
+     12.4 

25  23  5.-'.  2 
68  32  58.  2 
*6     3     3.  (i 
1257.  01 
1347.  35 

0.  367616 
9.968825 
9.99*116* 
3.  099337 
3.  129480 

• 

East  Signal  —  South  Base  . 

396.  08 

2.  598437 

VI. 

Court-house  
East  Signal  
South  Base  
Coiirt-hoiiHO  —  South  Base  
Court-house  —  East  Signal  

65  27  56.  6 
97  33  .111.2 

+       0.6 
+      6.2 

16  58     7.4 
65  27  57.2 
97  33  55.  4 
1236.  47 
1347.  35 

0.  534841 

9.  958!  N  15 
9.990203 
I!.  092183 
3.  1294*1 

North  Base  —  West  Signal 

353.73 

2.54*677 

VII. 

Naval  Observatory  .  
North  Base  
West  Signal  .......... 
Naval  Observatory—  West  Signal  .  . 
Naval  Observatory  —  North  Base  .  .  . 

13  31  15.8 
107  34  35.0 

+    in.:. 
+    21.6 

• 

r,s  r,:;  2".  1 

13  31  35.3 
107  34  56.6 
96.  63 
393.  85 

0.067431 

9.3691120 

ftttWU 

1.9*5128 
2.  595330 

OBSERVATIONS    OF   THE   ECLIPSE    OF   AUGUST   7,    1869. 


55 


No. 

1  iriHiinination. 

Ol)  served 
angles. 

Corr.  by 

adjust. 

Plane  angles 
and  distances. 

Logarithms. 

Kast  Si-nial     West  Signal 

o      /       // 

// 

f>79  29 

2  762894 

Naval  Observatory 

14     8  54  6* 

0  611835 

VIII. 

Ka.-l  Signal      
West  Si»-nal 

2  20  20.  8 
ifi:i  :u    '»  2 

8.4 
1C  2 

2  20  12.  4 
163  30  53  0 

8.  610374 
9  4r>->(Mi"i 

Naval  Observatory  —  West  Signal 
Naval  Observatory  —  East  Signal  . 

96.  63 
672.  SO 

1.985103 

2.H27694 

West  Signal     Court-house        .... 
Litehticld  <  >bservatory 

71    1  26  :> 

j_     45  o 

1257.  01 
71    2  11  5 

3.  099337 
0  024^35 

West  Signal 

74  47  43  3 

74  47  '!5  6 

<)  984521 

IX. 

(  'cinrl-lioiisc    
Litchfield  Observatory—  Conrt-b.ouse     . 

l.itehlield  Observatory  —  West  Signal      . 

3-1  10  12.9 
1282.  61 
746.  f.2 

9.  749469 
3.  108093 
2.  873041 

Kast  Signal  —  West  Signal 

579  29 

2  762896 

Litchl'ield  (  (bsrrvatorv 

32  22  27  0 

0  271284 

X. 

East  Signal     
West  Signal    
Litelilield  Observatory  —  West  Signal     . 
Litelilielil  Observatory  —  East  Signal 

136  21  :{").  9 
11   1")     7.9 

+     29.1 
+     20.  1 

136  22    5.  0 
11  15  28.0 
746.  52 
211.21 

9.  838864 
9.  290532 
2.  873044 
2.  324712 

In  the  triangle  Nnvsil  Observatory,  West  Signal,  Court  bouse,  we  have 


Plane  angles 
and  distances. 

Logarithms. 

Naval  Observatory  —  West  Signal  . 
West  Signal  —  Court-house  .  .  . 
Angle  at  West  Signal  

96.63 
1257.  01 
110  26    3.4 

1.985115 
3.  099337 

From  which  we  find  — 

Angle  at  Naval  Observatory  .  . 
Angle  at  Court-house  . 

1)5  33  10.3 
4     0  46  3 

Naval  Observatory  —  Court-house  . 

1293.  91 

3.  111905 

For  the  determination  of  the  azimuth  of  the  sides  of  the  triangles  we  have  the  following  obser. 
various  of  the  sun,  made  near  the  time  of  its  setting: 

August  9, 1889. — Theodolite  placed  over  West  Signal    Chronometer,  Negus  1319  which  is  6h 

IS'"  17-vs  fast  of  l(i,-i,l  mean  time. 


56 


REPORT    OF   PROFESSOR    HARKNESS. 


Telescope  direct. 

Object. 

Horizontal  circle. 

Transit  of  sun's— 

Vernier  A. 

Vernier  B. 

Court-house  .     . 
Snu     .... 
Sun     .... 
Sun      .... 
Court-house  .     . 

Means. 

O              III 

360       0       0 
84    20    40 
85      6  .30 

0      0 
21     30 
7    30 

2d  limb    . 
1st  limb   . 

/I.          III.          X. 

12       7       '.I 

*     31 

84    44      2 

0      0 

12      7    51.5 

360      0       0 

Telescope  reversed. 

Court-house  .     . 
Sun      .... 
Sun      .... 
Sun      .... 
Court-house  .     . 

Means. 

360      0       0 

86     18       0 
85    58      0 

0       0 
19       0 
59       0 

1st  limb    . 
2d  limb    . 

!•>    ic,     :, 

17     -JH 

86      8    30 

0       0 

12    16    42.5 

360      0      0 

For  the  reduction  of  tbese  observations  I  have  made  use  of  the  formula 


tan  M 


hill     n 
COS    / 


tan  A  = 


tan  t.  cos 


Sill 


—  M) 


where  A  is  to  be  taken  greater  or  less  than  180°,  according  as  t  is  greater  or  less  than 
A  =  azimuth  of  object,  counted  from  the  south  around  by  the 
S  =  declination  of  object. 
t  =  hour  angle  of  object. 
<p  =  latitude  of  place  of  observation. 

We  therefore  have 


Telescope 
direct. 

Telescope 
reversed. 

7i.    w.     x. 

/I.     HI.       K. 

Equation  of  time    .... 
t     .     .     

-     0    5    9.5 
5  44  24.2 

-    o    5    9.4 
5  53  15.  3 

ci                

+  15°38'40.  " 

+  15°38'34." 

t 

+  41  35  36. 

i    41  I!.",  ;j(j 

M   '.     .     . 

(<t>       M) 

+  76  21    5. 
—  34  45  29. 

+  84     0     3. 
—  42  24  27. 

99  21    5. 

100  4f>  21. 

Reading  of  horizontal  ciivle  . 

84  44     2. 

86     H  3d. 

South  point  of  circle   . 

345  22  57 

345  23     9 

Reading  to  Court-house    .     . 

360    0     0 

360     0     0 

Azimuth  of  Court-house  .     . 

14  37     3 

14  36  51 

OBSERVATIONS    OF   THE   ECLIPSE   OF   AUGUST   7,    1869. 


57 


The  azimuths  of  such  other  of  the  sides  as  were  required,  together  with  the  differences  of  lati- 
tude and  longitude,  have  been  computed  by  means  of  the  formula* 

—  d  L  =  K.  B.  cos  Z  +  K2.  C.  sin2  Z  +  h2  D 


A1.  K.  sin  Z 
cos  L1 


_  d  Z  =  d  M.  sin 


In  which 


N.  arc  1" 

,_         tan  L 

~~  2  N.  R.  arc  1" 

\  =  K.  B.  cos  Z,  or  first  term. 


R.  arc  1" 

f  e2.  sin  L.  cos  L.  arc  1" 
(1  — e2.  sin2L)| 

a.(l  — e2) 
(1  —  e2.  sin2  L)  f 


(1— 


a  —  equatorial  radius  of  the  earth  =  G377397.1G  meters. 
b  =  polar  radius  of  the  earth  =  635G078.9G  meters. 


I*- 

=v    «: 


— =  0.08169083 


K  =  the  given  geodetic  distance,  in  meters,  between  two  trigonometrical  points;  L  =  the  given 
latitude  of  the  first  point  ;  M  =  the  given  longitude  of  the  same  ;  Z  =  the  given  azimuth  of  the 
second  point  as  seen  from  the  first  :  the  azimuth  being  counted  from  the  south  around  by  the  west  ; 
L1,  M1,  Z'  =  the  required  latitude  and  longitude  of  the  second  point,  and  the  azimuth  of  the  first 
point  as  seen  from  it;  dL,  <Of,  «ZZ  =  the  required  differences  iu  latitude,  longitude,  and  azimuth  of 
the  two  points,  expressed  in  seconds  of  arc  ;  so  that 

L'=L  +dL 


Zl  =  Z  +(1Z  —  180°. 

Taking  the  values  of  A1,  B,  0,  and  D  from  the  Coast  Survey  tables,  the  following  are  the  results 
of  the  computations  : 

Azimuths  of  sides. 


West  Signal  to  Court-house 
Court-house  to  West  Signal      .     .     . 
Court-house  to  Naval  Observatory 
Naval  Observatory  to  Court-house 
Court-house  to  Litclifieltl  Observatory 
Litchfield  Observatory  to  Court-house 


14  36  57. 

194  36  47. 9 
190  36  1.6 

10  36  8.4 

228  47  0. 8 

48  47  28.4 


The  West  Signal  was  39".43  north,  and  13".70  =  0S.913  east  of  the  Court-house.  The  Naval 
Observatory  was  41".23  north,  and  10".28  =  Os.685  east  of  the  Court-house.  The  Litchfield  Observa- 
tory was  27".40  north,  and  41".66  =  2S.777  east  of  the  Court-house. 


8* 


'  Extracted  from  the  United  States  Coast  Survey  Report  for  1860,  p.  363. 


58 


REPORT    OF   PROFESSOR    ITARKNESS. 


GEOGRAPHICAL  POSITION  OF  THE  COURT  HOUSE  DOME. 

The  positions  of  all  the  temporary  observatories  must  finally  depend  upon,  and  be  referred  to, 
the  Court-house  dome,  for  the  determination  of  which  we  have  the  following  data  : 

In  a  letter  to  Commodore  B.  F.  Sands,  United  States  Navy,  dated  November  1, 18611,  Professor 
J.  E.  Hilgard  states,  that  the  office  reductions  of  the  observations  made  for  the  determination  of  the 
position  of  the  Coast  Survey  station  at  Des  Moines  have  not  yet  been  completed,  but  that  the  field 
computations  give 

Latitude  =  41°  35'  2".08 
Longitude  =  lh  29m  58N.29  west  of  Cambridge. 

The  reduction  from  the  station  to  the  center  of  the  Court-house  dome  is,  in  latitude  +  1".27,  and  in 
longitude  +  Os.05.  To  refer  the  difference  of  longitude  to  Washington,  I  have  employed  the  value 
of  Cambridge — Washington  obtained  from  the  joint  observations  of  this  observatory  and  the  United 
States  Coast  Survey  in  June,  1867,  namely,  O1'  2:5"'  HS.(IS  +  O.04. 

My  own  observations,  given  in  the  previous  pages  of  this  report,  place  our  temporary  observa- 
tory at  Des  Moines  in 

Latitude  =41°  35'  S-^'.O  ±  0".!K! 
Longitude  =  1"  G1"  1«8.05  ±  Os.05  west  of  Washington. 

On  the  evening  of  August  7,  while  1  was  exchanging  longitude  signals  with  the  observatory  in 
Washington,  Professor  Newcomb  and  Dr.  Peters  came  to  the  telegraph  office  and  compared  their 
chronometers  with  the  Washington  clock.  From  these  comparisons  Professor  Newcomb  finds  for 
the  Court-house  dome 

Longitude  =  I1'  6"'  16S.67, 

and  Dr.  Peters  finds  for  the  Litchfield  temporary  observatory 

Longitude  =  I1'  6'"  14S.02, 
in  both  cases  counting  from  the  dome  of  the  observatory  in  Washington. 

Applying  to  these  values  the  geodetic  differences  of  latitude  and  longitude  found  from  the  tri- 
angnlation,  we  get  for  the  Court-house  dome 


Latilndt'. 

Longitude. 

Authority. 

o       /         // 

ll.    III.          X. 

41     35    3.  3 

1    6    17.  26 

U.  S.  Coast  Survey. 

41    34  54.7 

16.74 

Harkncss. 

1C.  117 

Newcomb. 

16.80 

Peters. 

the  longitude  being  measured  from  the  center  of  the  dome  of  the  United  States  Naval  Observatory 
in  Washington.  I  am  rather  stiqirised  at  the  large  discrepancy  between  the  Coast  Survey  observers 
and  myself.  On  that  account  I  will  defer  all  further  discussion  as  to  the  position  of  the  Court-house 
until  I  make  my  report  on  the  reading  off  and  discussion  of  the  photographs  taken  during  the 
eclipse,  hoping  that  by  that  time  the  final  results  of  the  Coast  Survey  observations  may  be  avail- 
able. 

HEIGHT  OF  THE  DIFFERENT  STATIONS  ABOVE  THE  SEA. 

Colonel  J.  W.  Otley  gave  me  a  memorandum  stating  that  the  lines  of  level  run  for  the  Des 
Moines  Valley  railroad  show  that  its  track  at  the  depot  in  East  Des  Moines  is  310  feet  above  the 
Mississippi  River  at  Keokuk.  The  Mississippi  River  at  Keokuk  is  450  feet  above  the  level  of  the 
ocean.  Hence  the  railroad  track  at  the  depot  in  East  Des  Moines  is  7(i(i  feet  =  233.4  meters  above 
the  level  of  the  sea. 

Setting  up  the  theodolite  at  the  Des  Moines  Valley  railroad  depot,  the  axis  of  its  vertical  circle 
being  4.5  feet  =  1.37  meters  above  the  track,  I  measured  the  zenith  distance  of  the  ball  on  the  finial 
of  the  Court-house  dome  and  found  it  to  be  87°  41';  the  distance  from  the  theodolite  to  the  Court- 
house being  3,700  feet  =  1,128  meters. 


OBSERVATIONS    OF   THE    ECLIPSE    OF   AUGUST   7,    1809. 


Setting  up  the  theodolite  at  the  West  Signal,  with  the  axis  of  its  vertical  circle  1.37  meters 
above  the  ground.  I  measured  the  following  x.enith  distances: 

o       / 

Ball  mi  linial  of  Court -house .dome  -  88     38 

Floor  of  Litchtield  Observatory  89    47 

Floor  of  Naval  Observatory  88     16 

For  the  reduction  of  these  observations  I  have  employed  the  formula 
Difference  of  level  =  K.  cot  (A  —0.01356  K) 

in  which  K  is  the  distance  iu  meters  between  the  two  stations,  A  is  the  observed  zenith  distance, 
and  (0.01350  K)  is  seconds  of  arc. 

The  resulting  elevation  above  the  sea  of  the  different  stations  is  as  follows: 


Elevation. 

Object. 

Meters. 

Feet 

Cmn  t-lionse  dome       .... 

280.  5 

920.2 

Ground  at  West  Signal  .     .     - 

249.0 

816.9 

Naval  Observatory  floor  . 

253.3 

831.0 

LitrhlirM  Observatory  floor 

253.2 

830.  7 

MISCELLANEOUS  WORK  DURING  THE  ECLIPSE. 

Before  describing  the  observations  made  during  the  eclipse,  I  must  not  omit  to  mention  the  kind- 
ness and  forethought  of  his  honor  J.  H.  Hatch,  mayor  of  Des  Moines,  who,  without  any  solicitation 
on  our  part,  oil  the  afternoon  of  August  7,  sent  us  two  special  policemen,  Messrs.  Thomas  French 
and  —  -  Walker,  to  keep  spectators  from  crowding  too  closely  around  our  observatory.  They  did 
their  duty  most  efficiently,  preventing  the  occurrence  of  any  noise  in  the  neighborhood,  and  our 
thanks  are  due  both  to  Mayor  Hatch  and  to  them. 

As  I  had  decided  to  rest  the  astronomy  of  the  eclipse  entirely  upon  the  readings  to  be  obtained 
from  the  photographs,  I  attached  very  little  importance  to  the  making  of  optical  observations  of 
the  times  of  contact.  Nevertheless,  as  I  did  not  expect  to  be  otherwise  employed  at  the  beginning 
and  ending  of  the  eclipse,  I  at  one  time  contemplated  observing  the  first  and  last  contacts  by  means 
of  my  three-inch  telescope,  but  abandoned  that  plan  for  a  reason  which  will  presently  appear. 

The  course  which  seemed  to  me  to  afford  the  means  of  obtaining  the  greatest  accuracy  in  deter- 
mining the  beginning  of  the  eclipse  from  the  photographs,  was  to  commence  taking  pictures  about 
thirty  seconds  before  the  predicted  time  of  lirst  contact,  and  to  continue  taking  them  at  as  short 
intervals  as  possible,  until  the  moon  was  well  on  to  the  sun.  Upon  mentioning  this  plan  to  Dr. 
Curtis  he  readily  agreed  to  put  it  into  practice,  and  a  few  trials  showed  that,  with  the  number  of 
baths  and  assistants  at  his  disposal,  he  could  take  seven  or  eight  pictures  in  about  two  minutes, 
after  which  a  delay  of  two  or  three  minutes  would  occur  before  fresh  plates  could  be  sensitized. 
Owing  to  the  great  length  of  the  photographic  telescope,  it  was  found  impossible  to  remove  one 
sensitive  plate  and  insert  another  without  somewhat  disturbing  the  pointing  of  the  instrument,  and 
thus  rendering  a  new  pointing  necessary.  When  taking  pictures  at  the  rate  of  one  per  minute,  Dr. 
Curtis  found  no  difficulty  in  making  the  pointings  himself;  but  in  order  to  take  four  per  minute,  his 
whole  time  was  required  for  the  insertion,  timing,  exposure,  and  removal  of  the  plates,  and  there- 
fore, at  his  request,  I  made  the  pointings  of  the  telescope  during  the  time  that  pictures  were  being 
taken  at  such  short  intervals.  As  it  was  necessary  to  take  pictures  rapidly,  not  only  at  the  begin- 
ning of  the  eclipse,  but  at  the  end  also,  and  as  during  the  totality  I  was  engaged  with  the  spectro- 
scope, I  was  precluded  from  observing  the  time  of  any  of  the  contacts. 

After  the  first  two  minutes  of  the  eclipse  1  was  relieved  from  the  photographic  telescope,  and 


60 


REPORT    OF   PROFESSOR    HARKNESS. 


at  once  proceeded  to  attach  the  spectroscope  to  my  three-inch  telescope,  and  to  place  and  adjust  the 
necessary  counterpoises.  When  the  eclipse  had  so  far  progressed  as  to  reduce  the  sun  to  a  crescent, 
with  the  assistance  of  Professor  T.  H.  Saft'ord  I  adjusted  the  needle  in  the  finder  so  that  when  its 
point  fell  upon  a  horn  of  the  crescent  the  image  of  that  horn  fell  accurately  within  the  jaws  of  the 
spectroscope  slit.  This,  with  some  other  little  matters,  occupied  my  time  till  within  three  minutes 
of  the  totality,  when,  according  to  previous  arrangement,  I  called  Professor  Eastman,  who  was  to 
assist  me  in  making  the  spectroscope  observations  by  placing  and  keeping  the  needle  point  of  the 
finder  successively  upon  the  different  objects  to  be  examined. 

THE  SPECTROSCOPE  OBSERVATIONS. 

It  seems  to  me  that  one  of  the  desiderata  in  spectroscopic  observations  of  the  sun  during  total 
eclipses,  is  to  penetrate  as  low  down  towards  the  photosphere  as  possible.  In  order  to  accomplish 
this,  I  placed  the  slit  of  my  spectroscope  parallel  to  the  moon's  path,  and  clamped-  it  in  that  position, 
and  so  it  remained  during  all  my  observations.  Professor  Eastman's  eye  was  at  the  finder,  and 
mine  at  the  spectroscope,  at  least  a  minute  before  the  commencement  of  totality,  but  he  saw  no 
prominences.  Presently  the  sunlight  disappeared  like  the  snuffing  out  of  a  candle,  and  simulta- 
neously a  suppressed,  but  very  audible,  "Oh,  oh,"  arose  from  the  spectators  in  the  neighborhood. 
Instantly  he  placed  the  needle  point  on  the  prominence  marked  Fig.  2. 

1  on  Fig.  2,  and  I  recorded  its  spectrum  as  rapidly  as  possible. 
Then  we  passed  on  to  the  prominences  marked  2  and  3,  and 
their  spectra  were  successively  recorded  in  like  manner.  Next 
I  asked  him  to  give  me  the  corona,  and  he  placed  the  needle 
point  at  c1.  No  spectrum  appearing,  I  asked  him  to  try  another 
place,  and  he  placed  the  needle  at  c2.  Still  nothing  was  visible, 
and,  raising  my  head  from  the  instrument  for  the  first  time  since 
the  commencement  of  the  totality,  I  remarked,  "Can't  see  any 
spectrum;  don't  believe  we  will  get  any."  "Oh,  yes,  we  will," 
said  he.  At  that  instant  it  struck  me  that  perhaps  the  slit  was 
too  narrow,  so  I  opened  it  a  little,  and  then  again  placed  my  eve 
at  the  instrument.  In  the  meantime  he  had  put  the  needle 
point  on  a  very  bright  part  of  the  corona,  marked  <?  in  the  figure,  s 
and  I  at  once  saw  a  continuous  spectrum  about  as  bright  as  that  given  by  the  full  moon  on  a  clear 
night.  Remembering  that  the  observers  in  India,  in  August,  1868,  had  said  that  the  corona  gives 
a  continuous  spectrum  with  absorption  lines,  I  looked  very  carefully  for  them,  but  to  my  great  sur- 
prise I  could  see  none,  and  I  am  perfectly  satisfied  that  none  were  visible  in  my  instrument.  On 
the  contrary,  I  saw  an  absolutely  continuous  spectrum,  crossed  by  a  single  bright  line,  whose  posi- 
tion was  recorded. 

Once  more  raising  my  head  from  the  instrument,  I  glanced  upward  to  the  sky  and  saw  the 
moon  encircled  by  the  corona,  and  ac<x>nipauied  by  one  remarkably  large  prominence,  which  was 
attached  to  the  lower  limb  of  the  sun.  I  was  well  aware  that  the  red  prominences  are  sometimes 
visible  to  the  naked  eye,  but  this  one  was  so  exceedingly  conspicuous  that  it  could  not  fail  to  attract 
the  attention  of  the  most  careless  observer.  Almost  without  thinking  what  I  was  doing,  I  asked 
Professor  Eastman  to  point  the  spectroscope  to  it.  He  replied,  "You  have  had  it  already."  "Never 
mind,  give  it  to  me  again,"  said  I.  He  did  so,  and,  as  it  is  the  prominence  marked  3  in  the  figure, 
I  have  recorded  its  spectrum  in  the  column  headed  32  iu  the  table  below.  Professor  Eastman  then 
looked  down  to  the  chronometer  in  order  to  take  up  its  beat  for  the  purpose  of  noting  the  end  of 
the  totality.  As  he  did  so,  I  glanced  into  the  finder  so  that  I  might  get  some  idea  of  the  appear 
ance  of  a  total  eclipse  as  seen  through  a  telescope  of  small  power.  My  view  of  it  may  have  lasted 
five  or  ten  seconds,  certainly  not  more,  yet  the  magnificence  of  the  spectacle  is  so  indelibly  impressed 
upon  my  memory  that  it  will  be  years  ere  I  forget  it.  When  he  looked  up  from  the  chronometer  I 
replaced  my  eye  at  the  spectroscope,  and  asked  him  to  give  me  another  prominence.  He  put  the 
needle  point  on  the  one  marked  4  in  the  figure,  and  while  I  was  yet  engaged  in  recording  its  spec- 
trum there  came  a  sudden  burst  of  light,  and  Professor  Eastman  withdrew  his  eye  from  the  finder, 


OBSERVATIONS    OP   THE    ECLIPSE    OF    AUGUST    7,    1809.  61 

exclaiming,  "All  over."  It  was  too  true.  The  event,  for  the  proper  observation  of  which  we  had 
traveled  so  far,  and  spent  so  much  time,  aud  thought,  and  money,  had  come  and  gone,  and  now  it 
remains  for  the  scientific  world  to  judge  whether  or  not  we  made  the  most  of  our  opportunity. 

Professor  Eastman  at  once  sat  down  and  made  a  sketch  of  the  corona  and  prominences  as  they 
appeared  to  him  in  the  finder,  numbering  the  prominences  in  the  order  in  which  he  had  given  them 
to  me  in  the  spectroscope,  and  also  marking  the  places  on  the  corona  at  which  he  had  pointed.  I 
had  recorded  the  spectrum  observations  myself,  using  for  that  purpose  a  small  memorandum  book, 
writing  down  the  figures  without  looking  at  the  page,  arid  recording  only  one  spectrum  at  each  open- 
ing of  the  book — that  is,  when  I  had  recorded  one  spectrum  I  always  turned  the  leaf  before  record- 
ing another — thus  devoting  two  whole  pages  to  each  observation.  Such  being  the  state  of  the  case, 
all  that  was  necessary  in  order  to  identify  each  spectrum  with  the  prominence  to  which  it  belonged, 
was  for  me  to  mark  the  records  of  the  spectra  in  my  note  book  with  the  same  numbers  as  those 
employed  by  Professor  Eastman  on  his  sketch,  and  that  I  did  at  once ;  therefore  I  think  no  question 
can  ever  be  raised  as  to  the  prominences  to  which  the  spectra  belonged. 

At  the  time  of  making  these  observations  the  impression  left  on  my  mind  was  that  the  spectra 
given  by  the  different  prominences  differed  from  each  other,  not  only  in  the  number  of  the  lines,  but 
in  their  position  also.  It  was  not  till  four  hours  after  the  eclipse  that  I  had  time  to  compare  them 
with  each  other,  and  when  I  did  so,  arranging  them  as  in  the  table  below,  great  was  my  surprise  to 
find  that  the  difference  between  the  different  prominences  was  only  in  the  number  of  lines,  and  not 
in  their  position  at  all.  Before  passing  to  the  consideration  of  the  lines,  however,  it  will  be  best  to 
mention  some  particulars  relative  to  the  adjustments  of  the  spectroscope,  and  the  method  pursued 
in  making  the  observations. 

Some  minutes  before  the  beginning  of  the  totality  the  micrometer  scale  was  so  adjusted  that 
its  fiftieth  division  coincided  exactly  with  the  mean  of  the  two  sodium  lines  which  together  form  the 
line  D ;  and  the  slit  was  opened  to  such  a  width  as  to  give  fine,  sharp  definition  of  all  the  lines.  The 
instrument  remained  in  that  condition  till  the  observation  of  the  spectrum  of  the  corona,  before 
which  the  slit  was  opened  a  little  wider.  After  that  none  of  the  adjustments  were  altered  in  the 
slightest  until  the  next  day.  Immediately  after  the  end  of  the  totality  the  scale  reading  of  the  line 
D  was  tested  ;  first  by  observing  the  position  of  the  black  line  in  the  solar  spectrum,  and  then  by 
placing  the  Hame  of  an  alcohol  lamp,  whose  wick  contained  a  little  common  salt,  before  the  object- 
glass  of  the  telescope  and  observing  the  position  of  the  resulting  bright  line.  In  both  cases  the 
reading  was  exactly  fifty  divisions,  thus  proving  that  the  instrument  had  kept  its  adjustment  during 
the  observations  of  the  prominences  and  corona.  Then  the  following  readings  of  the  positions  of 
some  of  the  lines  in  the  solar  spectrum  were  taken : 


C  36.2 

D  50.0 

E  67.9 

b  71.5 


F  84.8 

115.0 
116.0 

G         117.8 


After  that  the  spectroscope  was  detached  from  the  telescope.  Next  morning,  before  any  of  the 
adjustments  had  been  altered  in  the  slightest,  a  sodium  flame  was  put  before  the  slit  of  the  spectro- 
scope and  the  width  of  the  resulting  bright  line  was  observed  to  be  0.8 -of  a  scale  division.  From 
the  angular  value  of  one  division  of  the  scale,  together  with  the  focal  length  of  the  collimating  lens 
of  the  slit,  it  can  easily  be  shown  that- when  the  width  of  the  bright  sodium  line  is  one  division,  the 
width  of  the  slit  is  0.0037  of  an  inch.  Therefore,  at  and  after  the  observation  of  the  spectrum  of 
the  corona  the  width  of  the  opening  of  the  slit  was  0.0030  of  an  inch ;  in  observing  the  spectra  of 
the  prominences  before  that  it  was  a  little  narrower. 

As  my  instrument  gives  a  spectrum  about  330  minutes  in  length,  the  whole  of  which  is  visible 
at  once  in  the  field  of  view  of  its  telescope,  it  is  admirably  adapted  for  rapid  work.  But  when  the 
telescope  is  adjusted  to  give  the  best  possible  definition  of  the  lines  near  D,  those  near  H,  although 
still  quite  distinct,  are  nevertheless  slightly  out  of  focus,  and  by  moving  the  eye  across  the  eye-piece 
their  scale  reading  can  be  made  to  vary  a  little.  To  have  adjusted  the  focus  accurately  on  each  line 
observed  during  the  eclipse  would  have  involved  an  expenditure  of  time  not  for  one  moment  to  be 


62 


REPORT    OF   PROFESSOR    HARKNESS. 


thought  of,  and,  as  each  scale  division  corresponds  to  somewhat  less  than  two  minutes,  I  therefore 
judged  it  best  to  observe  as  many  spectra  as  possible,  noting  the  position  of  each  bright  line  to  the 
nearest  half  of  a  scale  division  only,  and  trusting  that,  from  the  closely  approximate  positions  thus 
obtained,  all  the  lines  might  be  found  at  any  time  after  the  eclipse  with  a  sufficiently  powerful  instru- 
ment. 

Now  let  us  pass  to  the  consideration  of  the  observations.  They  are  given  in  the  table  below, 
the  first  column  of  which  contains  the  letters  of  such  of  the  lines  as  are  so  designated ;  the  columns 
headed  1,  2,  31,  32,  and  4,  contain  respectively  the  spectra  of  the  prominences  marked  1,  2,  3,  and  4> 
in  Fig.  2,  the  column  headed  31  containing  the  record  of  the  first,  and  that  headed  32  the  record  of 
the  second  spectrum  observed  from  the  prominence  3 ;  the  column  headed  "Corona"  contains  the 
reading  of  the  bright  line  in  the  spectrum  of  the  corona. 


1 

2 

3' 

Coroiia. 

3- 

4 

Meau. 

Kirch, 
scale. 

\Vav.j 
length. 

c 

46.0 

37.0 

36.5 

36.0 

36.0 

36.3 

693 

656.9 

D 

50.0 

50.5 

50.0 

50.0 

50.1 

1007 

589.4 

67.5 

67.0 

67.0 

66.5 

66.5 

67.  r> 

67.  (1 

1497 

531  1.  0 

. 

70.5 

. 

70.5 

Kill 

520.1 

F 

85.0 

. 

. 

si.  0 

84.5 

84.5 

2069 

Mr.  e 

-     - 

•      - 

-     - 

114.0 

1  1  1.  5 

114.  '.> 

8776 

436.9 

The  number  40,  recorded  on  the  line  C  in  column  1,  is  evidently  a  misreading  of  ten  divisions. 
It  should  doubtless  have  been  3G.  Making  this  correction,  and  bearing  in  mind  that  the  readings 
were  made  at  a  glance,  te  the  nearest  half  division  only,  without  stopping  to  verify  them,  I  think 
it  will  be  admitted  that  all  the  numbers  on  any  one  horizontal  line  of  the  table  are  sufficiently  near 
to  each  other  to  warrant  me  in  assuming  them  to  be  readings  of  one  and  the  same  bright  line.  In 
other  words,  during  the  whole  of  the  totality  I  only  observed  six  lines;  the  double  line  D  being 
counted  as  a  single  line  because  it  so  appeared  to  inc.  I  have  therefore  taken  the  mean  of  the  num- 
bers on  each  horizontal  line,  and  placed  them  in  the  column  headed  "Mean."  These  I  consider  to 
be  the  observed  scale  readings  of  the  bright  lines,  and  in  the  columns  headed  "  Kirch,  scale  "  and 
"  Wave  length,"  I  have  given  the  corresponding  readings  of  Kirchhotf 's  scale,  and  the  wave  lengths 
expressed  in  milliouths  of  a  millimeter. 

Now  let  us  examine  the  position  of  each  prominence  at  the  time  its  spectrum  was  taken.  The 
spectrum  of  1  was  observed  as  soon  after  the  beginning  of  the  totality  as  possible,  but  a  glance  at 
Fig.  2  shows  that  it  lay  very  far  from  the  path  of  the  moon's  center,  and  therefore  its  base  was  not 
visible.  It  gave  four  bright  lines.  2  was  next  examined.-  It  lay  almost  exactly  in  the  path  of  the 
moon's  center,  but  by  this  time  she  had  advanced  so  far  that  probably  it  was  not  visible  more  than 
half-way  down  to  its  base.  It  gave  three  bright  liues.  Then  the  t-elescope  was  pointed  at  3,  which, 
being  on  the  southwestern  limb  of  the  sun  and  distant  from  the  path  of  the  moon's  center,  had  only 
just  begun  to  be  much  uncovered.  Its  summit  was  all  that  was  visible,  and  it  gave  but  two  bright 
lines.  After  spending  some  time  on  the  corona,  3  was  again  examined.  As  the  moon  had  moved 
forward  considerably  the  prominence  was  uncovered  much  further  down  towards  the  sun,  and  now 
it  gave  no  less  than  six  bright  lines.  Finally  4  was  pointed  at,  and  as  it  lay  almost  exactly  in  the 
path  of  the  moon's  center,  and  the  totality  ended  while  it  was  yet  under  examination,  the  spectro- 
scope must  have  penetrated  down  to  its  very  base.  I  recorded  five  bright  lines  from  it,  but  I  am 
not  certain  that  there  were  no  more,  because  I  was  not  done  with  it  wheu  I  was  stopped  by  tin- 
flood  of  returning  sunlight.  The  first  thing  that  would  be  likely  to  strike  a  person  on  looking  at 
the  observations  is  that  no  two  prominences  gave  the  same  spectrum ;  but  I  think  it  is  now  evident 
that  this  does  not  indicate  any  difference  of  constitution  among  them.  On  the  contrary,  the  num- 
ber of  lines  visible  seems  to  depend  solely  on  the  part  of  the  prominence  examined.  If  we  take  the 
spectrum  from  near  the  summit  we  get  but  few  lines ;  if  we  take  it  lower  down  we  get  more  lines, 
but  those  that  we  found  at  the  top  are  still  there ;  if  we  take  it  near  the  base  all  the  lines  we  had 
before  remain,  and,  in  addition,  some  new  ones  appear.  Therefore  I  infer  that  these  observations 


OBSERVATIONS   OP   THE    ECLIPSE    OF   AUGUST   7,    1869.  63 

indicate  that  all  the  prominences  possess  nearly,  if  iiot  precisely,  the  same  physical  constitution,  but 
that  that  constitution  undergoes  a  gradual  change  from  their  bases  toward  their  summits.  If  such 
is  the  case,  then,  when  the  spectrum  of  a  prominence  is  examined  with  the  slit  of  the  spectroscope 
perpendicular  to  the  limb  of  the  sun,  the  bright  lines  should  appear  of  different  lengths.  This 
applies  to  my  observations  of  the  prominences  2  and  4,  but  whether  or  not  they  gave  lines  of  dif- 
ferent lengths  I  am  unable  to  say.  I  remember  distinctly  that  some  of  the  prominences  did  do  so, 
but  unfortunately  I  made  no  memorandum  which  will  enable  me  to  identify  the  particular  ones. 

The  next  question  which  presents  itself  is,  what  are  the  substances  which  gave  rise  to  the 
observed  bright  lines?  In  order  to  identify  these  lines  in  the  most  certain  manner  possible,  I  was 
very  anxious  to  observe  with  my  instrument  the  spectra  of  hydrogen,  iron,  and  magnesium,  but 
unfortunately  I  did  not  succeed  in  obtaining  a  sufficiently  powerful  induction  coil.  1  am  therefore 
obliged  to  resort  to  the  published  results  of  other  investigators. 

Professor  W.  Gibbs,*  on  the  authority  of  Pliicker,  gives  for  the  wave  lengths  of  the  hydrogen 
lines,  H«  =  653.3,  Rft  =  484.3,  H^=433.9 ;  and  on  the  authority  of  Angstrom,  H/?=1797.3,  H^=1604.3. 
H«  and  lift  are  known  to  coincide  respectively  with  Fraunhofer's  C  and  P,  for  which  I  have  adopted 
the  wave  lengths  050. 8  and  486.5.  In  order  to  render  Pliicker's  values  identical  with  these,  his  II« 
must  be  multiplied  by  1.0054,  and  his  11,5  by  1.0045.  Multiplying  his  HJ-  by  this  last  quantity,  it 
becomes  435.9,  which  I  shall  consider  as  the  result  of  his  observations.  Angstrom's  wave  lengths 
are,  given  in  j-ujnlooou  °^  a  Pai'is  inch,  and  in  order  to  reduce  them  to  millionths  of  a  millimeter,  I 
have  assumed 

1  Paris  inch  =  27.0700  millimeters. 

They  therefore  give,  H,S  =  480.5,  11^  =  434.3.  Taking  the  .mean  of  Plh'ckcr's  and  Angstrom's  meas- 
ures, we  have  for  the  wave  lengths  of  the  hydrogen  lines 

II«  =  G5G.S 
H/S  =  48G.5 
Hr  =  435.1 

Assuming  the  wave  lengths  of  the  lines  sodium  ft  and  «  to  be  respectively  590.53  and  589.88, 
Kayett  gives  as  the  wave  length  of  the  yellow  bright  line  in  the  solar  spectrum,  588.27  =  1016.8  of 
Kirchhoff's  scale.  Throughout  this  report  I  have  adopted  Na.  ft  =  590.04,  Na.  a  =  589.43.  It  there- 
fore results  that  the  wave  length  of  the 

Yellow  bright  line  =  587.9 

From  a  paper  "On  the  Spectra  of  some  of  the  Chemical  Elements,"  by  Mr.  William  Huggins,| 
I  have  extracted  the  following  positions  of  certain  bright  lines  in  the  spectrum  of  iron : 

Huggins's  scale.  Wave  length. 
1560  530.7 

.1574  529.4 

1582  528.8 

The  lines  1560  and  1574  are  quite  faint,  but  1582  is  very  bright.  I  have  made  use  of  Professor 
W.  Gibbs's  tables  §  to  convert  the  readings  of  Mr.  Hnggins's  scale  into  wave  lengths. 

I  have  not  any  table  of  the  spectrum  of  magnesium,  but  its  principal  lines  are  known  to  coin- 
cide with  the  components  of  Fraunhofer's  line  6,  the  wave  lengths  of  which,  as  deduced  by  Profes- 
sor W.  Gibbs  from  Ditscheiner's  and  Angstrom's  measurements,!]  are  as  follows: 

518.73 
517.70 
517.15 

»  American  Journal  of  Science,  [2,]  XXXIX,  217.  }  Philosophical  Transactions,  1864,  p.  139. 

t  Comptes  Rendus,  LXVIII,  320,  February,  1869.  §  American  Journal  of  Science,  [2,]  XLVII,  194. 

II  American  Journal  of  Science,  [2,]  XLIII,  1,  and  XLV,  298. 


64 


REPORT    OF   PROFESSOR   HARKNESS. 


For  convenience  of  reference  the  results  are  collected  in  the  following  table,  the  first  column  of 
which  contains  my  observed  wave  lengths  of  the  various  bright  lines  given  by  the  corona  and  prom- 
inences, together  with  the  possible  error  of  each  wave  length,  deduced  upon  the  supposition  that 
the  observed  scale  reading  of  any  line  may  be  in  error  to  the  extent  of  half  a  division ;  the  second 
column  contains  the  wave  lengths  found  above  for  the  bright  lines  in  the  spectra  of  certain  chemi- 
cal elements : 


Wave  lengths  of 
bright  lines. 

AV:ivi>  lengths  of  chemical  ele- 
ments. 

656.  9  ±  3.  2 

656.  8      Hydrogen. 

589.  4  ±  2.  1 

587.  9      Unknown,  (sodium  f) 

530.71 

530.0  ±1.4 

529.  4  I  Iron. 

528.  8  J 

520.1  ±1.4 

518.  7      Magnesium. 

487.5  ±1.0 

486.  5      Hydrogen. 

435.  9  ±  0.  7 

435.  1       Hydrogen. 

Owing  to  the  very  moderate  dispersive  power  of  my  spectroscope  the  iron  lines  528.8  and  529.4 
would  certainly  coalesce,  and  530.7  would  probably  coalesce  with  them,  and  appear  as  a  single 
rather  thick  line,  which  was  what  I  actually  sa\v.*  Bearing  in  mind  what  is  already  known  of  solar 
physics,  I  think  there  can  scarcely  be  a  doubt  that  the  bright  lines  in  the  prominences  were  pro- 
duced by  the  substances  whose  names  stand  respectively  on  the  same  horizontal  lines  with  the 
observed  wave  lengths  in  the  table  above.  The  identification  of  the  lines  is  therefore  complete. 

Physical  constitution  of  the  corona. — On  this  subject  many  different  theories  have  been  proposed, 
but  they  may  all  be  divided  into  three  general  classes:  1.  Those  which  attribute  the  formation  of 
the  corona  to  the  passage  of  the  sun's  rays  through  the  earth's  atmosphere.  2.  Those  which  attrib- 
ute its  formation  to  the  passage  of  the  solar  rays  through  a  supposed  lunar  atmosphere.  3.  Those 
which  consider  the  corona  as  an  envelope  of  some  kind  surrounding  the  sun. 

Against  theories  belonging  to  the  first  class  there  are  two  objections  which  seem  to  me  to  be 
fatal.  The  moon's  shadow,  at  the  point  where  it  enters  the  earth's  atmosphere,  usually  has  a  diame- 
ter of  one  hundred  miles  or  more,  and  if  it  were  possible  for  an  observer  placed  within  that  shadow 
to  see  the  illumination  of  the  atmosphere  outside  of  it,  the  appearance  presented  would  be  that  of 
a  halo  having  an  interior  diameter  much  greater  than  the  size  of  the  moon.  At  the  commencement 
of  the  totality  the  moon  would  be  within,  and  tangent  to,  this  halo,  and  as  the  eclipse  progressed 
she  would  move  across  its  interior  till  she  finally  reached  its  other  edge,  at  which  instant  the  totality 
would  end.  It  is  almost  needless  to  say  that  no  such  phenomenon  has  ever  been  seen,  the  only 
known  effect  of  the  illumination  of  the  surrounding  atmosphere  being  to  produce  a  blush  of  light  in 
the  distant  horizon.  Besides,  as  the  illumination  of  the  surrounding  atmosphere  is  due  to  ordinary 
sunlight,  if  it  is  the  cause  of  the  corona  its  spectrum  should  show  Fraunhofer's  lines,  while  my 
observations  prove  that  it  does  not  do  so.  I  looked  specially  for  them,  but  could  see  none,  although 
the  spectrum  was  sufficiently  bright  and  the  width  of  the  slit  was  only  0.0030  of  an  inch. 

Against  theories  belonging  to  the  second  class  there  are  equally  fatal  objections.  For  many 
years  astronomers  have  exhausted  all  their  ingenuity  in  devising  methods  for  the  detection  of  a 
lunar  atmosphere,  but  as  yet  without  success.  Mr.  Huggins's  observation  of  the  occupation  of 
e  Piscium,  on  January  4,  1865,  through  the  spectroscope,!  is  probably  the  most  delicate  optical  test 
that  can  be  applied,  but  even  it  failed  to  show  any  trace  of  such  an  atmosphere.  I  am  aware  that 
the  brightening  seen  along  the  limb  of  the  moon  on  photographs  of  solar  eclipses  has  been  attributed 
by  some  to  the  effect  of  a  lunar  atmosphere;  but  Mr.  Airy  has  shown f  that,  even  if  such  an  atmo- 

*  I  do  not  wish  to  be  understood  as  stating  that  the  bright  line  in  the  corona  is  either  double  or  triple.  I  only  assert 
that,  so  far  as  my  observations  are  concerned,  such  may  be  the  case ;  and  that,  at  all  events,  I  think  it  will  be  found  to 
coincide  with  one,  or  more,  of  the  three  iron  lines  in  question. 

t  Monthly  Notices,  Royal  Ast.  Soc.,  XXV,  60.  }  Monthly  Notices,  Royal  Ast.  Soc.,  XXIV,  13. 


OBSERVATIONS    OB'    THE    ECLIPSE    OF   AUGUST    7,    1869.  65 

sphere  existed,  it  could  not  produce  this  effect;  and  Dr.  Curtis  shows  in  his  report  on  the  eclipse 
under  discussion  that  it  is  due  to  the  diffraction  of  the  sunlight  caused  by  the  moon's  limb.  In 
short,  there  is  not  a  shadow  of  reason  to  believe  that  any  such  thing  as  a  lunar  atmosphere  exists  ; 
but  if  it  did,  and  the  corona  was  due  either  to  reflection  or  refraction  of  the  sunlight  by  it,  then  the 
spectrum  of  the  corona  should  show  Fraunhofer's  lines,  which,  as  I  have  already  stated,  is  not  the 
case. 

An  examination  of  the  photographs  of  totality,  fac-similes  of  which  are  given  in  Plates  X  and 
XI,  shows  that  as  the  moon  advanced  the  corona  was  progressively  covered ;  and  this,  taken  in 
connection  with  the  spectroscope  observations,  forces  us  to  conclude  that  it  must  be  an  envelope  of 
some  kind  surrounding  the  sun.  It  has  been  objected  that  it  cannot  be  a  solar  atmosphere  because 
its  form  is  too  irregular.  Plates  IX,  X,  XI,  and  XII  show  that  during  the  present  eclipse  its  gen 
era!  outline  was  trapezoidal,  the  angles  being  in  middle  latitudes  ;  in  other  words,  it  did  not  extend 
so  far  from  the  body  of  the  sun  either  at  the  equator  or  at  the  poles  as  it  did  about  latitude  45°. 
Observations  of  the  barometer  made  at  the  level  of  the  sea  show  that  the  earth's  atmosphere  has  a 
very  similar  form,  which,  I  think,  is  a  sufficient  answer  to  the  objection.  It  has  also  been  objected 
that  if  the  corona  is  an  atmosphere  surrounding  the  sun,  it  should  reverse  the  bright  lines  which 
can  always  be  seen  in  the  chromosphere  by  using  a  spectroscope  of  sufficient  dispersive  power. 
This  is  somewhat  difficult  to  answer.  The  general  appearance  of  the  spectrum  of  the  corona,  as  I 
saw  it,  is  very  well  represented  on  Plate  V.  The  brightness  of  the  continuous  portion  was  about 
equal  to — perhaps  slightly  less  than — that  of  the  spectrum  which  I  get  from  the  moon  in  the  same 
instrument ;  and  I  am  perfectly  convinced  that  there  were  no  absorption  lines.  I  looked  particu- 
larly for  them,  and  the  light  was  sufficiently  intense  and  the  slit  sufficiently  narrow  for  me  to  have 
seen  them  if  they  had  been  present.*  The  bright  line  was  tolerably  conspicuous,  but  it  did  not 
stand  out  so  glaringly  as  the  bright  lines  in  the  prominences.  So  far  as  a  single  observation  can  be 
depended  upon,  it  seems  to  me  that  this  one  tends  to  prove  that  the  corona  is  a  highly  rarefied 
self-luminous  atmosphere  surrounding  the  sun,  and  that  it  is  composed  principally  of  iron  in  the 
state  of  incandescent  vapor.  Probably  the  selective  absorption  of  the  continuous  portion  of  the 
spectrum  is  not  sufficiently  strong  to  do  more  than  slightly  dim,  without  actually  reversing,  the 
bright  lines  of  the  chromosphere.  But  with  the  bright  line  at  67.0  divisions  of  my  scale  the  case 
is  different.  If  I  have  rightly  identified  its  wave-length,  it  does  reverse  the  solar  spectrum,  for  the 
rays  whose  wave-lengths  are  530.7  and  528.8  are  respectively  identical  with  the  dark  lines  at  1487.7 
and  1508.6  of  KirchhofFs  map. 

It  has  very  recently  been  suggested  that  the  bright  line  in  the  corona  probably  coincides  with 
one  of  the  bright  lines  in  the  spectrum  of  the  aurora,  and  that  therefore  the  corona  is  nothing  else 
than  a  permanent  solar  aurora.  On  the  nights  of  April  15  and  June  6,  1869,  Professor  Joseph 
Winlock  observed  the  following  bright  lines  in  the  spectrum  of  the  aurora  :  t 

Mr.  Huggins'  scale.  Wave  length. 
1280  (brightest)  557.1 

1400  544.6 

1550  531.5 

1680  near  F.  521.0 

2640  near  G.  463.9 

Angstrom  gives  J  for  the  wave-length  of  the  brightest  line  in  the  aurora  556.7,  agreeing  very 
well  with  the  result  above.  I  found  for  the  wave-length  of  the  bright  line  in  the  corona  530.0,  while 
Professor  Winlock  finds  for  one  of  those  in  the  aurora  531.5.  I  scarcely  think  that  the  two  are 
identical,  but  even  if  they  are,  although  it  may  prove  that  the  glowing  gas,  or  vapor,  is  the  same  in 
both  cases,  it  certainly  does  not  prove  that  in  the  case  of  the  corona  the  heating  power  is  an  elec- 
trical discharge,  which  is  generally  admitted  to  be  the  cause  of  the  aurora.  It  is  worthy  of  remark 

*  It  is  now  nearly  certain  that  if  hydrogen  gas  is  gradually  heated  until  it  becomes  luminous  it  will  first  yield  a 
continuous  spectrum,  which,  when  the  temperature  becomes  sufficiently  intense,  will  suddenly  change  into  the  well- 
known  spectrum  consisting  of  three  or  four  bright  lines.  May  not  the  continuous  spectrum  of  the  corona  be  due  to 
hydrogen  which  is  much  cooler  than  that  forming  the  red  prominences  f 

tAmer.  Journal  of  Science,  [2,]  XLVIII,  123.  tP°gg-  Annalen,  May,  1869. 

-9* 


66  REPORT    OF   PROFESSOR    HARKNESS. 

that  the  lines  1400  and  1680  of  Professor  Winlock's  spectrum  of  the  aurora  .coincide  respectively 
with  the  positions  of  an  iron  and  a  chromium  line  in  Mr.  Hnggius'  tables.  Have  we  iron  vapor  in 
the  upper  regions  of  our  own  atmosphere  f 

Physical  constitution  of  the  red  prominences. — A  glance  at  Plate  V  shows  that  all  the  promi- 
nences which  I  observed  presented  the  bright  line  whoso  wave-length  is  530.0,  together  with  a  faint 
continuous  spectrum  ;  but  as  those  were  dne.to  the  light  radiated  from  that  portion  of  the  corona 
lying  between  me  and  the  prominences,  there  remain  only  three  hydrogen  lines,  one  magnesium 
line,  and  the  unknown  line  near  that  of  sodium,  which  were  produced  by  the  prominences  them- 
selves. These  lines  have  all  been  frequently  observed  before,  and  it  is  also  well  known  that  the 
magnesium  never  rises  very  high  above  the  chromosphere,  but  so  far  as  I  am  aware  the  following- 
fact  is  new.  At  the  base  of  a  prominence  we  find  all  the  lines,  but  as  we  ascend  from  the  surface 
of  the  chromosphere  we  lose  first  the  magnesium  and  the  blue  hydrogen  line,  then  the  green  hydro- 
gen line,  then  the  unknown  yellow  line,  and  only  the  red  hydrogen  line  extends  to  the  very  summit 
of  the  prominence.  This  has  a  very  important  bearing  on  a  remark  by  Mr.  De  La  Hue,*  who  lays 
great  stress  on  the  fact  that  he  found  on  one  of  his  photographs  of  the  total  solar  eclipse  of  July  18, 
1860,  the  image  of  a  prominence  which  he  had  not  seen  in  his  telescope.  Hearing  in  mind  that  the 
red  and  yellow  portion  of  the  spectrum  contains  most  of  the  luminous  rays,  while  it  is  destitute  of 
chemical  ones,  it  will  be  evident  that  the  spectroscope  observations  tend  to  prove  that,  owing  to 
their  summits  not  containing  any  chemical  rays,  the  prominences  will  not  appear  so  high  on  a  pho 
tograph  as  they  do  when  viewed  in  a  telescope  ;  and  also  that  any  prominence  which  can  be  photo- 
graphed must  be  visible  to  the  eye  through  a  telescope  of  sufficient  power,  while  there  may  be 
prominences  perfectly  visible  to  the  eye  which  cannot  be  photographed.  Tliis  is  in  direct  opposi- 
tiod  to  Mr.  De  La  Eue's  statement,  but  it  agrees  perfectly  with  Professor  Eastman's  observations 
of  the  present  eclipse,  for  his  sketch  shows  all  the  prominences  which  are  to  be  found  on  the 
photographs. 

The  question  naturally  presents  itself,  why  do  the  hydrogen  lines  disappear  successively  in  the 
manner  indicated  above  1  So  far  as  we  know  it  must  be  the  effect  either  of  pressure  or  of  temper- 
ature. Under  a  pressure  of  360  millimeters,  and  with  a  very  intense  spark,  hydrogen  gives  a  con- 
tinuous spectrum.  At  a  somewhat  less  pressure  the  spectrum  breaks  np'into  bands,  H/3  and  H/ 
being  the  broadest ;  if  the  gas  be  considerably  rarefied  these  bands  become  perfectly  sharply  defined 
lines.  If  the  reduction  of  pressure  be  still  further  continued,  the  red  line,  H«,  gradually  disappears, 
while  H/J,  though  fainter,  remains  well  defined.  Hence  the  disappearance  of  the  lines  in  the 
prominences  cannot  be  an  effect  of  pressure,  and  is  probably  due  to  decrease  of  temperature.  The 
highest  temperature  procurable  by  artificial  means  is  that  yielded  by  the  electric  spark  which  will 
produce  all  the  hydrogen  lines.  Next  to  it  ranks  the  oxy  hydrogen  flame,  the  spectrum  of  which, 
and  also  that  of  the  hydrogen  flame,  I  was  enabled  to  examine  by  the  kindness  of  Brevet  Lieutenant 
Colonel  J.  J.  "Woodward,  assistant  surgeon  United  States  Army.  In  both  cases  the  result  was  the 
same.  Only  three  lines  were  visible,  namely :  that  of  sodium  and  the  lines  calcium  «  and  /?.  Not 
.the  slightest  trace  of  the  hydrogen  lines  appeared.  I  therefore  "conclude  that  the  temperature  of 
the  summits  of  the  red  prominences  is  greater  than  that  of  the  oxy-hydrogeu  flame,  which  is  about 
2500°  Centigrade  =  4532°  Fahrenheit,  and  less  than  that  of  the  electric  spark,  the  heat  of  which  is 
entirely  unknown. 

To  recapitulate,  the  new  facts  developed  by  the  spectroscope  observations  recorded  in  this 
report  are 

I.  The  corona  gives  an  absolutely  continuous  spectrum,  crossed  by  a  single  bright  line  whose 
wave-length  is  approximately  530.0. 

II.  In  ascending  from  the  chromosphere  the  hydrogen  lines  in  the  red  prominences  disappear 
in  the  order  H^,  H/3,  Ha  ;  Ha  being  the  only  line  found  at  the  very  summit  of  the  prominences. 

III.  The  physical  constitution  of  the  red  prominences  appears  to  be  the  same  in  all. 

From  these  facts  I  consider  the  following  conclusions  highly  probable,  if  they  are  not  actually 
proved. 

A.  The  corona  is  a  highly  rarefied  self-luminous  atmosphere  surrounding  the  sun,  and,  perhaps, 
principally  composed  of  the  incandescent  vapor  of  iron. 

*  Phil.  Transactions,  1862,  p.  404. 


OBSERVATIONS    OP    THE    ECLIPSE    OF    AUGUST   7,    1869.  67 

B.  The  temperature  of  the  summits  of  the  red  prominences,  at  a  distance  of  a  hundred  thou- 
sand miles  from  the  sun's  surface,  exceeds  4500°  Fahrenheit — a  heat  more  than  sufficient  to  vaporize 
iron. 

SCALE  OF  TINTS. 

The  scale  of  tints,  with  which  the  colors  of  the  prominences  seen  around  the  sun  during  the 
totality  were  compared,  is  shown  in  Plate  V,  and  is  composed  of  the  following  pigments: 

a  and  b,  pure  carmine,  c  and  d,  carmine  and  cadmium,  e,  Vandyke  brown,  fandg,  Van- 
dyke brown  and  cadmium.  A,  pure  cadmium,  i,  sepia  and  cadmium. 

CONCLUSION, 

All  my  instruments  and  apparatus  worked  in  the  most  satisfactory  manner,  and  were  I 
ordered  to  observe  another  solar  eclipse  I  would  make  but  two  change*  in  my  outfit.  In  place  of 
the  small  pocket  surveying  instruments  I  would  take,  if  possible,  a  five  or  six.  inch  theodolite ;  and 
I  would  have  my  spectroscope  altered  so  as  to  employ  a  collimating  lens  of  shorter  focus  between 
the  prism  and  the  slit — thus  bringing  the  body  of  the  instrument  nearer  to  the  telescope,  and 
avoiding  the  use  of  such  heavy  counterpoises.  In  the  examination  of  the  corona  and  prominences, 
I  believe  that  more  spectra  can  be  observed  during  the  time  of  totality  by  having  a  steady  and 
reliable  assistant  to  point  the  finder,  than  if  a  driving  clock  is  employed  and  the  spectroscope 
observer  makes  the  pointings  himself. 

In  view  of  the  very  great  importance  which  the  question  of  the  physical  constitution  of  the 
corona  has  assumed,  I  regret  exceedingly  that  there  was  a  failure  in  the  use  of  my  polarizing  appa- 
ratus, and  that  I  am  unable  to  report  any  results  from  it. 

I  shall  at  once  proceed  to  design  the  large  micrometer  necessary  for  reading  off  the  photographs 
taken  by  Dr.  Curtis  during  the  eclipse,  and  as  soon  as  the  instrument  is  completed  I  will  make  the 
measurements  on  the  negatives,  reduce  and  discuss  the  results,  and  place  my  report  on  the  subject 
in  your  hands,  so  that  it  may  be  published  without  any  unnecessary  delay. 
I  am,  Commodore,  most  respectfully, 

\VM.  HARKNESS, 
1'rofennor  of  Mathematics,  United  States  Navy. 

Commodore  B.  F.  SANDS,  U.  S.  N., 

Superintendent  United  States  Naval  Observatory,  Washington,  D.  C. 


REPORT    OF   PROFESSOR    HARKNESS. 


SCHEDULE  A. 

Observations  of  the  sun  for  Time,  made  at  the  temporary  United  States  Naval  Observatory  at  Des 
Moines,  Iowa,  by  Prof.  Wm.  Harkness,  U.  8.  N.,  icith  the  Sextant  Staekpole  cfc  Bro.  No.  937,  Mer- 
curial Artificial  Horizon  Ha.  1,  and  Chronometer  T.  S.  &  J.  D.  Negus  No.  1.310. 

[NOTE. — The  barometer  employed  was  an  aneroid  belonging  to  Prof.  J.  R.  Eastman;  and  0.38  of  an  inch  must  be 
subtracted  from  all  its  recorded  readings  in  order  to  free  them  from  constant  errors.] 


SUN         .        .        .        JULY  23,  1869.                SUN         .        .        .        JULY  23,  ls(>9. 

• 

Index  Corr. 

E 

Index  Corr.,  &c. 

On  Arc  =  6>. 

Off  Arc  =  4)i. 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  o. 

Off  Arc  =  t)i. 

•       /      a 
•29  10 
30 
20 

O      '        " 

4  26  30 
10 
25 

t     ii 
29  10 
20 
15 

O      '        " 

4  26  10 
10 
10 

+          2    9.6 
+              10.4 

t 

+          2  17.5 
+               8.9 

-f-          2  20 

+          2  26.  4 

Means 
Index  Corr.,  &c. 

Q 

Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 

Q 

Refraction 
Parallax 

2  Altitude. 

Chronometer. 

O      '         '/ 

60  30    0 
45    0 
61     0    0 
60  30    0 
45    0 
61    0    0 

h.  m.     a. 
1  55  35.0 
56  15.1 
56  55.6 
58  23.6 
59    2.9 
59  42.3 

O       '          '/ 

54  30    0 
15    0 
0    0 
54  30    0 
15    0 
0    0 

/I.     »!.         8. 

11     6    3.2 
ti  44.  0 
7  23.5 
8  50.5 
9  31.  5 
10  11.3 

60  45    0.0 
+          2  20.0 

1  57  39.  1 

54  15    0.0 
+         2  26.  4 

11    8    7.3 

o 
Ther.    76.0 

in. 
Bar.      29.  58 

O        '           /' 

=  69  58  49.  3 

h.  m.     s. 
7  33  20.  1 

.  +      6  10.6 

60  47  20.  0 
1  33.0 

+               7.3 

54  17  26.  4 
1  44.5 
+               7.5 

Polar  distance  of  object       .     . 

Local  Apparent  Time     .     .     . 
Equation  of  Time      .... 

Local  Mean  Time       .... 
Time  by  Chronometer     .     .     . 

Chronometer  fast  of  Local  M.  T. 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Timi 

Local  Mean  Time 
Time  by  Chromm 

Chronometer  fast 
These  observatu 

0        /          " 

object      .      .     =70     3  34.  4 

h.  in.      s. 
ime     ....       4  43  48.  7 

)                                         -L        R   11    9 

.       7  39  30.  7 
.       1  57  39.  1 

4  49  59  9 

rlrl1     . 

.     11     8    7.3 

.       6  18    8.4 

of  Lorn!  M.T.   .       6  18    7.  4 
us  wi'i-«  made  after  noon. 

These  observations  were  made  before  noon. 

OBSERVATIONS    OF    THE   ECLIPSE    OF   AUGUST   7,    1869. 
SCHEDULE  A— Continued. 


69 


SUN          ....         JULY  23. 

SUN          ....        JULY  24. 

On  Arc  —  u. 

Off  Arc  =  u'. 

On  Arc  =  a. 

Off  Arc  =  a1. 

t      n 

ot" 

t     it 
29  20 
20 
30 

0      '        " 

4  25  40 
40 
45 

Index  Corr.             +          2  17.  5 

E                              +               7.  7 

Index  Corr              +          2  27.  5 
E                              +8.6 

Index  Corr.,  &c.     +          225.2 

Index  Corr.,  &c.    !+          2  36.  1 

2  Altitude. 

Chronometer. 

2  Altitude. 

Chronometer. 

O       '         II 

47  45    0 
30    0 
15    0 
47  45    0 
30    0 
15    0 

« 
h.  m.    e. 

11  24  11.3 

24  51.  8 
25  31.7 

27     0.5 
27  38.5 
28  20.  8 

0        /          II 

52  30    0 
45    0 
53    0     0 
52  30    0 
45    0 
53    0    0 

h.  m.     s. 
1  34  50.6 
35  31.5 
36  12.0 
37  40.0 
38  19.0 
39    0.0 

Means                           47  30    0.0 
Index  Corr.,iVc.     -f          225.2 

11  26  15.8 

Moans                           52  45    o.  0 
Index  Corr.,  &c.    ;+          2  36.  1 

1  36  55.  5 

0 

Thfi  .       86.  8 

O        1        II 

—  70     3  43.  3 

/I.    III.       9. 

.      5    1  56.7 
-  +      6  11.2 

.0 

Thcr.    77. 

in. 

Bar.       29.  46 

o"    /        /' 
=  70  11  11.2 

h.    Ml.         8. 

.      7  12  34.8 
+      6  11  8 

Q                                   47  32  25.  2 
Kofi-action                             2     1.2 
Parallax                   -f-                ~-7 

Q                                    '>••>  47  36.  1 
Refraction                             1  49.8 
Parallax                  -f-               7.6 

Polar  distance  of  object 

Local  Apparent  TimS 
Equation  of  Time 

Local  Moan  Time       .... 

Polar  distance  of  object       .     . 

Local  Apparent  Time     .... 
Equation  of  Time 

Local  Mean  Time 

-      5    8    7.  9 

7  18  46  6 

Time  by  Chronometer     .     .     . 
Chronometer  fast  of  Local  M.  T. 

-     11  26  15.8 

Time  by  Chronometer    .     .     . 
Chronometer  fast  of  Local  M.  T. 

1  36  55.  5 

6  18    7.9 

.       6  18    8.9 

These  observations  \vere  made  after  noon. 

These  observations  were  made  before  noon. 

70 


REPORT    OF   PROFESSOR   HARKNESS. 


SCHEDULE  A— Continued. 


SUN          ....        JULY  26. 

SUN          ....        JULY  26. 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  a. 

Off  Arc  =  u1. 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  .=  u. 

Off  Arc  =  u1. 

t     a 
29  10 
10 
10 

Q       1          II 

4  26  10 
25  50 
26  10 

i     it 
29  10 
25 
25 

0      '        " 

4  26  10 
10 
0 

+          2  23.  4 
+              12.0 

+          2  16.6 
+              12.0 

+          2  35.4 

+          2  28.6 

Means 
Index  Corr.,  &c. 

0 

Refraction 
Parallax 

2  Altitude. 

Chronometer. 

» 

Means 
Index  Corr.,  &c. 

n 

Refraction 
Parallax 

2  Altitude. 

Chronometer. 

o     '       " 
67  30    0 
45    0 
68    0    0 
67  30    0 
45    0 
68    0    0 

h.  m.     s. 
2  16  29.  5 
17  10.0 
17  50.6 
19  19.5 
19  58.  0 
20  39.2 

0        /        II 

68    0    0 
67  45    0 
30    0 

A.  in.     s. 
10  30  38.  4 
31  19.5 
31  59.2 

67  45    0.0 
+          2  35.4 

2  18  34.  5 

o 
Ther.     70. 

iw. 
Bar.      29.  52 

O            t              H 

=  70  37  39.  1 

A.  m.     s. 
.      7  54  12.0 

-f      6  12  7 

0 

Ther.     81.  0 

in. 
Bar.      29.  49 

O        '          " 

=  70  42  13.  8 

/I.    HI.         8. 

67  47  35.4 
1  22.3 

+               7.0 

Polar  distann  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chrononi 

Chronometer  fast 
These  observatio 

object 
me 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chronom 

Chronometer  fast 
These  obiwrvatio 

abject       -      - 
me     ... 

8    0  24.  7 

eter    .     .     . 
of  Local  M.  T. 

.       2  18  34.  5 

Bter     .     .     . 

.f   l.orul  M.T. 

- 

.       6  18    9.8 

- 

as  were  made  before  noon. 

is  were  made  after  noon. 

OBSERVATIONS    OF    THE    ECLIPSE    OF   AUGUST   7,    1869. 


71 


SCHEDULE  A— Continued. 


SUN         ....        JULY  26. 

SUN           ....        JULY  27. 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  a. 

Off  Arc  =  u'. 

Index  Corr. 
E 

Index  Corr.,  <fec. 

On  Arc  =  u. 

Off  Arc  =  u<. 

o     /      " 

/    // 

o     /       // 

+          2  16.0 
+               11.3 

+          2  18.3 
+              13.0 

+          2  27.9 

+          2  31.  3 

Means 
Index  Corr.,  <fcc. 

U 

Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  <fec. 

Q 
Refraction 

Parallax 

2  Altitude. 

Chronometer. 

o     /       // 
64  45    0 
30    0 
15    0 
64  45    0 
30     0 
15     0 

ll.    III.       8. 

10  36  33.0 
37  12.8 
37  52.5 
39  20.  8 
40     1.  5 
40  41.0 

0       /          " 

72  30     0 
45     0 
73     0    0 
72  30     0 
45     0 
73     0     0 

h.  m.    s. 
2  30  41.  0 
31  22.0 
32     1.0 
33  29.  8 
34     9.7 
34  50.0 

64  30    0.0 
+          2  27.  9 

10  38  36.  9 

72  45    0.  0 
+          2  31.3 

2  32  45.6 

O          '              // 

=  '70  42  17.  8 

li.  m.    ». 
.      4  14  ]5.5 

_|_      6  12  5 

O          /            // 

=  70  51  18.  7 

h.  m.    s. 

.      8    8  22.  8 

-  +      6  12.2 

64  32  27.  9 

1  25.8 
+                7.1 

72  47  31.  3 
1  14.5 

+                6.8 

Polar  distance  of 

Local  Apparent  TJ 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chronom 

Chronometer   last 

These  obser\  atio 

object 
me 

Polar  distance  of  < 

Local  Apparent  Ti 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chrouom 

Chronometer  fast  < 
These  observatioi 

)bject 
me 

4  20  28.  0 

8  14  35  0 

?ter     .      .     . 
jf  Local  M.  T. 

.     10  38  36.9 

jter    .     .     . 
>f  Local  M.  T. 

-       2  32  45.6 

.       6  18    8.9 

.      6  18  10.6 

is  were  made  after  noon. 

is  were  made  before  noon. 

72 


REPORT   OF   PROFESSOR   HARKNESS. 


SCHEDULE  A— Continued. 


SUN          ....        JULY  27. 

SUN           ....        Jri.V  2K. 

Index  Corr. 
E 

Index  Corr.,  «Stc. 

On  Arc  =  u. 

Off  Arc  =  u'. 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  u. 

OH'  Are  —  (A 

i     u 
29  15 
30 
20 

O      '           '/ 

4  26    0 
5 

0 

1        II 

29  20 
30 
30 

0      '        a 

4  26  10 

111 
0 

+          2  18.3 
+              13.7 

+          2  13.3 
+              11.3 

+          2  32.  0 

+          2  24.  6 

Means 
Index  Corr.,  &c. 

B 

Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Means 
[nili-x  (,'OIT.,  &e. 

a 
Refraction 

Parallax 

2  Altitude. 

Chronometer. 

O        i    .11 

74  45    0 
75    0    0 
15    0 
74  45    0 

75     (1     0 
15     II 

A.  m.     a. 
2  36  43.  8 
37  25.0 
38    5.9 
39  34.5 
40  14.5 
40  55.  0 

o     /       a 
64  30    0 
45     0 
65     0     0 
64  30     (I 
45     0 
().,     (I     0 

h.   m.     ». 
2    9  58.  0 
10  37.0 
11  17.8 
12  46.2 
13  2<i.  2 
14     6.  3 

75     0    0.0 
+       .  2  32.0 

2  38  49.8 

64  45    0.0 
+          2  24.  6 

2  12     1.9 

o 
Ther.    74. 

in. 

Bar.      29.  53 

U          /              // 

=  70  51  22.  1 

A.  m.    s. 
.       S  14  26.  8 

+      6  12.  2 

Ther.     HI. 

in. 
liar.     29.  58 

0        '        II 

=  71     4  57.4- 

/(.   Ml.       8. 

.       7  47  38.4 
.  +      6  11.2 

75    2  32.  0 
1  11.6 
+                6.7 

64  47  24.  6 
1  28.2 
+                7.1 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  l>y  Clironnm 

Chronometer  fast 
These  observatio 

object 
me      ... 

Polar  dislanre  uf 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chronom 

Chronometer  fait 
These  obsenalin 

object      .     . 
me 

8  20  39  0 

.       7  53  49.6 

eter     .     .     . 
of  Local  M.  T. 

.       2  38  49.  8 

eter     . 
of  Local  M.T. 

.       2  12    1.9 

.       6  18  10.8 

.       6  18  12.3 

us  were  made  before  noon. 

MS  were  made  before  noon.  •   . 

OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST   7,    1869. 


73 


.SCHEDULE  A— Continued. 


SUN           ....        JULY  28. 

SUN           ....        JULY  28. 

Index  Corr. 
E 

Index  Con\,  &c. 

On  Arc  =  u. 

Off  Arc  =  u'. 

Index  Corr. 
E 

Index  Corr.,  &e. 

On  Arc  =  u. 

Off  Arc  =  o,'. 

/     // 
29  10 
10 
10 

o     /     // 
4  25  50 
26     0 
25  40 

/     // 

o     /      // 

+        2  ::n.  0 
4-            11.3 

+          2  30.  t' 

+               10.  7 

+          241.3 

+          2  40.7 

Means 
Index  Corr.,  &c. 

U 
Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Means 

Index  Corr.,  &c. 

Q 

liVfi  action 
Parallax 

2  Altitude. 

Chronometer. 

O         1        II 

65    0     0 
64  45    0 
30     0 
65    0     0 
64  45     (I 
30    0 

/I.    lit.         8. 

10  34  21.2 
35    2.2 
35  42.3 
37     9.2 
37  49.  5 
38  30.  1 

Q          1          II 

62    0    0 
61  45    0 
30    0 
62    0    0 
61  45    0 
30    0 

A.  m.      8. 
10  42  24.  5 
'    43    4.5 
43  44.  0 
45  11.0 
45  52.  0 
46  32.  3 

64  45     0.0 
+          2  41.3 

lit  :i»;  -j:>.  >' 

61  45    0.0 
+          2  40.7 

10  44  28.0 

O         '          // 

=  719  52.  6 

/i.  m.      s. 
.       4  12    4.4 

.  +      6  10.  7 

0 

Ther.    74. 

in. 
Bar.      29;  57 

=  71    9  57.2 

/I.    111.         X. 

.       4  20     6.4 
.   +       6  10.7 

64  47  41.  3 
1  26.5 

+               7.1 

61  47  40.7 
1  31.7 

+                7.2 

Polar  distance  of  < 

Local  Apparent  Ti 
Equation  of  Time 

Local  Mean  Time 
Time  by  Clironom 

Chronometer  fast 
These  ohservatioi 

ibjcct       -     - 
me      ... 

Polar  distance  of 

Local  Apparent  Ti 
Equation  of  Time 

Local  Mean  Time 
Time  by  Clironom 

Chronometer  fast  ( 
These  observatim 

ibjeet 
me 

;tcT     . 
)f  Local  M.  T. 

-       4  18  15.  1 
.     10  36  25.  8 

4  26  17.  1 

iter     .      .     . 
)f  Local  M.  T. 

.     10  44  28.0 

.       6  18  10.7 

.      6  18  10.9 

is  were  made  after  noon. 

is  were  made  after  noon. 

10* 


74 


•REPORT    OF   PROFESSOR   HARKNESS. 


SCHEDULE  A— Continued. 


SUN                                               JULY  29. 

SUN         ....         JULY  29. 

Index  Con-. 
E 

Index  Corr.,  &c. 

On  Arc  =  a. 

Off  Arc  =  <A 

Index  Corr., 
E 

Index  Corr.,  &c. 

Ou  Arc  =  u. 

Off  Arc  =  o>. 

i    a 
29  10 
15 
10 

Q        I           II 

4  26    0 
25  50 
55 

i    n 

0      '       " 

+          2  26.  6 
+              10.9 

+          2  26.  6 
+              10.9 

+          2  37.5 

4-         2  37.  5 

Means 
Index  Corr.,  &c. 

Q 

Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 

a 

Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Q          1          II 

63  15    0 
.30    0 
45    0 
63  15     0 
30     0 
45     0 

ft.  m.    H. 
2    7  23.  0 
8    2.5 
8  40.6 
10  11.0 
10  50.  4 
11  30.  0 

O         /         /' 

63  45    0 

30    0 
15    0 
03  45    0 
30    0 
15    0 

h.   in.     8. 
10  36  55.  8 
37  34.8 
38  15.0 
39  43.  0 
40  23.  0 
41     3.8 

63  30    0.0 
+          2  37.5 

2    9  26.2 

f,:i  30     0.0 
+          2  37/5 

10  38  59.  2 

o 
Ther.     65.  5 

in. 
Bar.      29.70 

O         i         ii 

=  71  19    5.  3 

ll.    M.      8. 

.       7  45     4.3 
-   +       6    9.5 

O         '         ft 

—  71  24  10.  1 

7l.    TO.      8. 

.       4  14  38.5 

4-      6    8.  9 

63  32  37.5 
1  29.8 
+               7.2 

<•>::  :w  37.5 
1  28.3 

+               7.2 

* 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chronon 

Chronometer  fust 
These  observatio 

object       .     . 
me      .     .     . 

Polar  distance  of 

Local  Apparent  T 
Ki|ii:ilion  of  Time 

Local  Mean  Time 
Time  l>,y  ('hronom 

Chronometer  last 
These  observatio 

iibjcct 
me 

7  51  13  8 

4  20  47.4 

eter     .      .     . 
of  Local  M.  T. 

.      2    9  26.2 

eter           .     .           10  38  59.2 

of  Local  M.  T. 

.       6  18  12.4 

.       6  18  11.8 

ns  were  made  before  noon. 

us  were  made  after  noon. 

OBSERVATION'S   OF   THE   ECLIPSE    OF   AUGUST   7,    1869. 


75 


SCHEDULE  A— Continued. 


SUN          ....         JULY  29. 

SUN                                               JULY  30. 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  u. 

Oil'  Arc  =  ul. 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  u. 

".Off  Arc  =  6il. 

HMM 

i     it 
29    5 
10 
15 

Of" 

4  25  50 
26    0 
0 

i    n 

O        t        ft 

+          2  26.  6 
+              10.5 

+          2  24.2 
+              13.8 

+          2  37.  1 

+          2  38.  0 

Means 
Index  Corr.,  &c. 

il 
Befractiou 

Parallax 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 

Q 
Refraction 

Parallax 

2  Altitude. 

Chronometer. 

O        '        " 

61  45    0 
30    0 
15     0 
61  45     0 
30    0 
15    0 

h.  m.    s. 
10  42  16.5 
42  57.  0 
43  37.  0 
45     3.0 
45  44.  0 
46  24.2 

o     '      " 
75  45     0 
76     0    0 
75  30    0 
75  45    0 

A.  m.    8. 
2  41  46.5 
42  25.  0 
43  56.5 
44  37.2 

61  30    0.0 

+          2  37.  1 

10  44  20.  3 

75  45    0.  0 
+          2  38.  0 

2  43  11.3 

c 
Th.-i-.     7  !.  O 

in. 
Bar.       29.  63 

o      /      •' 
=  71  24  13.  3 

h.  m.     n. 
.       4  19  59.  8 

4-      6    8.9 

0         /         /.' 

=  71  33  53.  9 

h.  m.    s. 
8  18  52.  1 

.  +      6    7.2 

61  32  37.  1 
1  32.0 
+                7.2 

75   17  38.0 
1  10.9 
4-                6.7 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chronom 

Chrouiimeler  last 
These  obscrvatio 

object 
me 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Clirononi 

Chronometer  fast 
These  observatio 

object       .     . 
me      ... 

4  26    8.7 

.      8  24  59.  3 

eter     . 
of  Local  M.  T. 

.     10  44  20.  3 

eter     . 
of  Local  M.  T. 

.      2  43  11.3 

.      6  18  11.6 

.      6  18  12.0 

ns  were  made  after  noon. 

is  were  made  before  noon. 

76 


REPORT    OF    PKOFESSOR   HAEKNESS. 


SCHEDULE  A— Continued. 


SUN           ....        JULY  30. 

SUN           ....        JULY  30. 

Index  t'orr. 
E 

Index  Corr.,  &c. 

On  Arc  =  u. 

Off  An-  =  (A 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  u. 

Off  Arc  =  w'. 

/     // 
29  20 
20 
20 

C       '        " 

4  25  50 
55 
50 

i     a 
29  10 
20 
15 

Q        1          It 

4  2<i  10 
1(1 
5 

+          2  24.  2 
+              14.4 

+          2  18.4 
+              10.6 

4-          2  38.6 

+          2  29.0 

Means 
Index  Corr.,  &e. 

H 
Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 

a 
Befraction 

Parallax 

2  Altitude. 

Chronometer. 

Q          t          II 

77  45    0 
78    0    0 
15    0 
77  45     0 
78    0     0 
15    0 

It.  m.      a. 
2  47  11.5 
47  51.8 
48  33.6 
50    3.0 
50  44.  9 
51  25.0 

O        '        " 

62    0    0 
(il  45    0 
30    0 
62    0    0 
61  45    0 
30    0 

II.    III.        8. 

10  40  46.5 
41  27.0 
42    6.9 
43  35.  0 
44  15.0 
44  55.5 

78    0    0.0 
+          2  38.  6 

2  49  18.3 

61  45    0.0 
+          2  29.0 

10  42  51.  0 

c 
Ther.    71. 

i«. 
Bar.      29.  69 

0        '          II 

=  71  33  57.  6 

h.  m.      s. 
.       8  24  58.  6 

-f      6    7.2 

O        1          II 

—  71  38  46.7 

Jl.    }ll.         8. 

.       4  18  32.  0 
.  +      6    6.  4 

78    2  38.  6 
1    8.2 
+               6.6 

61  47  29.  0 

1  30.8 
+               7.2 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Thin 

Local  Mean  Time 
Time  by  Clirouon 

Chronometer  fast 
These  observatii 

object 
ime     .     .     . 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chronoir 

Chronometer  fast 
These  nhservatii 

object      .     . 
ime      .     .     . 

eter     .     .     . 
of  Local  M.  T. 

eter     . 
of  Local  M.  T. 

.      8  31     5.  8 
.      2  49  18.  3 

.      4  24  38.4 
.     10  42  51.  0 

.       6  18  12.5 

.      6  18  12.6 

us  were  made  before  noon. 

us  were  made  after  noon. 

OBSERVATIONS   OF   THE    ECLIPSE    OF    AUGUST   7,    1869. 


77 


SCHEDULE  A— Continued. 


SUN           ....        JULY  30. 

SUN           ....        JULY  31. 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  u. 

Off  Arc  =  cA 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  u. 

Off  Arc  =  u'. 

/     // 
29  10 
30 
35 

0       '        " 

4  26    5 
5 
15 

/     // 
29  10 
15 
25 

O       '         '/ 

4  26    0 
0 
10 

+          2  13.4 
+              10.1 

• 

+          2  20.0 
+              13.7 

+          2  23.  5 

+          2  33.  7 

Mem 

Index  Corr.,  &c. 

U 
Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &e. 

a 

Refraction 

Parallax 

2  Altitude. 

Chronometer. 

O        I       II 

60    0    0 
59  45    0 
30    0 
CO     0    0 
59  45    0 
30    0 

It.    III.        S. 

10  46    7.  5 
46  48.2 
47  28.0 
48  55.  0 
4!)  36.5 
50  15.3 

O         /         '/ 

75     0     0 
.  15     0 
30     0 
75     0    0 
15    0 
30     0 

/I.    III.        S. 

2  40  33.  5 
41  14.0 
41  54.5 
43  23.  5 
44    4.3 
44  44.5 

59  45    0.0 

+          2  23.  5 

10  48  11.  8 

75  15    0.  0 
+          2  33.7 

2  42  39.  0 

o 
Ther.    79. 

i«. 
Bar.      29.  61 

o      /        // 
=  71  38  -19.7 

/I.    III.         8. 

4  23  53.  5 

+      664 

o      /       // 
=  71  48  39.9 

h.  m.      a. 
.       8  18  20.  8 

.   +       6    4.4 

59  47  23.  5 
1  34.5 
+                7.3 

75  17  33.7 
1   10.4 

+               6.8 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Cbronom 

Chronometer  fast 
These  olisurvutiu 

object      .     . 
me      .     .     . 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chronom 

Chronometer  fast 
These  observatio 

object       .     . 
me 

4  29  59.9 

8  24  25  2 

eter     .     .     . 
of  Local  M.  T. 

.     10  48  11.8 

eter     .     .     . 
of  Local  M.  T. 

.      2  42  39.0 

-       6  18  11.9 

.      6  18  13.8 

is  were  made  after  noon. 

IN  were  made  before  noon. 

78 


EEPOKT   OF   PROFESSOR   HARKNESS. 


SCHEDULE  A— Continued. 


SUN         .        .        .        .        JULY  31. 

SUN           ....        JULY  31. 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Are==u. 

Off  Arc  =  <j1. 

Index  Corr. 
t 
E 

Index  Con-.,  &c. 

On  Arc  =  u. 

Off  Arc  =  cj'. 

/     // 

o     /     a 

/     // 
29  20 
30 
35 

O        /          " 

4  26  10 
15 
10 

+         2  20.0 
+              14.4 

+          2  12.0 
+              10.5 

Chronometer. 

+          2  34.4 

+          2  22.5 

Means 
Index  Corr.,  &c. 

n 

Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 

a 

Refraction 
Parallax 

2  Altitude. 

Q          1          II 

78*30    0 
45    0 
79    0    0 
78  30    0 
45    0 
79    0    0 

7l.    Ml.         8. 

2  50    3.  0 
50  44.5 
51  26.  0 
52  54.  5 
53  36.  0 
54  17.2 

o      /     /' 
62    0    0 
61  45    0 
30     0 
62    0    0 
61  45    0 
30    0 

li.  m.      s. 
10  39  55.  2 
40  35.  3 
41  15.5 
42  44.2 
43  24.  5 
44    3.2 

78  45    0.  0 
+          2  34.  4 

2  52  10.  2 

61  45    0.0 
+         2  22.5 

10  41  59.6 

o 
Ther.    72.5 

iii. 
Bar.      29.  68 

0        '          " 

=  71  48  45.  9 

7l.    III.        8. 

.       82751.9 
.  +      6    4.4 

O          f            ft 

=  71  53  38.  7 

/(.    III.        S. 

.       4  17  42.9 
+       <>    3  4 

78  47  34.  4 
1     6.1 
+               6.6 

61  47  22.  r, 
1  28.8 
+               7.3 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chronoui 

Chronometer  fast 
These  obaervatio 

object 
line      .     .     . 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Clironom 

Chronometer  last 
These  obsenalio 

object       .      . 
me 

eter     . 
if  Local  M.  T. 

8  33  56  3 

.       4  23  46.3 

.     10  41  59.6 

eter     - 
of  Local  M.  T. 

.      2  52  10.2 

.       6  18  13.9 

.      6  18  13.3 

us  were  made  before  noon. 

is  were  made  after  noon. 

OBSERVATIONS   OF   THE   ECLIPSE    OP   AUGUST   7,    I8G9. 


79 


SCHEDULE  A— Continued. 


SUN         ....         JULY  31. 

SUN        ....        AUGUST  4. 

Index  Corr. 

E 

Index  Con-.,  &c. 

On  Arc  =  u. 

Off  Arc  =  u1. 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  u. 

Off  Arc  =  o>. 

i      u 

0       '         II 

i      n 
29  20 
30 
30 

O       /         ii 

4  26  10 
15 
10 

+          2  12.0 
+             10.0 

+           '.>  10.8 
+               13.  0 

+          2  22.  0 

+          2  23.  8 

Menus 
Index  Corr.,  &c. 

11 
Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 

Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Q        1          II 

59  15    0 

59    0    0 
58  45    0 
59  15    0 
59    0    0 
58  45    0 

li.  m,    n. 
10  47  18.  0 
47  57.  0 
48  37.8 
50    5.5 
50  46.  0 
51  25.8 

O       '          II 

72    0     0 
15     0 
30    0 
72     0    0 
15    0 
30    0 

h.  m.    s. 
2  35  41.  b 
36  22.3 
37    2.1 
38  32.  1 
39  12.7 
39  53.  1 

59    0    0.  0 
+          2  22.  0 

10  49  21.7 

72  15    0.0 
+       •  2  23.  8 

2  37  47.  3 

o 
Ther.    81.  5 

in. 
Bar.       29.  60 

0         i        II 

=  71  53  43.  2 

ft.    Mi.       8. 

.       4  25    4.7 
-  +      6    3.4 

o 
Ther.    80.5 

in. 
Bar.       29.  47 

c      /      /' 
=  72  50  38.  8 

h.  m.    s. 
.      8  13  44.  8 

-   +       5  47.4 

59    2  22.  0 
1  33.8 
+               7.4 

72  17  23.8 
1  12.6 

+               6.9 

Polar  distance  of 

Local  Apparrnl  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chronom 

Chronometer  fast 
These  obstT\  al  in 

abject 
me 

Polar  distance  of  < 

Local  Apparent  Ti 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chrouom 

Chronometer  fast 
These  observatioi 

)bjeet 
me 

4  31     81 

8  19  32  2 

eter     .     .     . 
)f  Local  M.  T. 

.     104921.7 

•ter     .     .     . 
if  Local  M.  T. 

.       2  37  47.  3 

.       6  18  13.6 

.       6  18  15.  1 

is  were  made  after  noon. 

is  were  made  before  noon. 

80 


REPORT   OF   PROFESSOR    IIARKNESS. 


SCHEDULE  A— Continued. 


SUN      ....       AUGUST  4. 

SUN       ....       AUGUST  7. 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  u. 

Off  Arc  =  t»>. 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  u. 

Off  Arc  =  u'. 

i    n 
29  20 
25 
30 

O       '        'I 

4  26    5 
25  55 
26    5 

i    n 
29  45 
40 
50 

O       1       II 

4  26  15 
20 
10 

+          2  16.6 
+              10.4 

+          2    0.0 
+              12.5 

+          2  27.0 

+         2  12.5 

Means 
Index  Corr.,  &c. 

Q 

Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &.c. 

Q 
Refraction 
Parallax 

2  Altitude. 

Chronometer. 

o      /      " 
61    0    0 
60  45    0 
30    0 
61    0    0 
60  45    0 
30    0 

h.  m.    s. 
10  38  52.  0 
39  32.  5 
40  12.8 
41  40.5 
42  21.2 
43    1.0 

O       1       II 

70  15    0 
30    0 
45    0 
70  15    0 
30    0 
45    0 

h.  m.    s. 
2  33  28.  8 
34  10.5 
34  50.5 
36  20.  3 
37     1.4 
37  42.0 

60  45    0.0 
+          2  27.0 

10  40  56.7 

70  30    0.0 
+         2  12.5 

2  35  35.6 

o 
Ther.    89.  5 

in. 
Bar.      29.  39 

o      /      " 
=  73  40    5.  4 

/i.    in.     *. 
.      8  11  50.0 

+      5  28.4 

60  47  27.0 

1  28.4 
+               7.3 

70  32  12.  5 
1  18.5 

+              6.8 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chronom 

Chronometer  fast 
These  observatio 

o     /       " 
abject       .     .     =  72  56    3.  5 

A.  m.      s. 
ime      -     -     -     -      4  10  5,r..  6 
j-     r,  4r,  4 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chronom 

Chronometer  fast 
These  observatio 

object 
me      .     .     - 

•  -     -     -     - 

eter     -     .     . 

of  Local  M.  T. 

4  22  41.  0 
.     10  40  56.7 

8  17  18.4 

eter     .     .     . 
of  Local  M.  T. 

.      2  35  35.  6 

.       6  18   15.7 

.       6  18  17.2 

ns  were  made  after  noon. 

as  were  made  before  noon. 

OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST   7,    1869. 


81 


SCHEDULE  A— Continued. 


SUN  *  .         .         .         .        AUGUST  7. 

SUN       .         -         -         -        AUGUST  7. 

Index  Corv. 
E 

Index  Corr.,  &c. 

On  Arc  =  a. 

Off  Arc  =  iA 

Index  Corr. 
E 

Index  Corr.,  &c. 

On  Arc  =  u. 

Off  Arc  =  <A 

/        n 

o    /      " 

/     // 
29  30 
25 
25 

o     '      // 
4  26    5 
0 
5 

+          2    0.0 
+              IS.  6 

+          2  15.0 
+              16.1 

+          2  13.6 

+          2  31.  1 

Meana 

Index  Corr.,  &c. 

It 
Refraction 
Parallax 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 

Q 

Refraction 
Parallax 

2  Altitude. 

Chronometer. 

o      /      // 
74    0     (1 
15     0 
30     0 
74     0     0 
15     0 
30     0 

/I.  «l.        8. 

2  43  42.2 
44  23.2 
4.')     4.4 
46  34.5 
47  15.4 
47  56.7 

O         '       " 

85     0     0 
84  45     0 
3(1     (1 
85     0     0 
84  45    0 
30    0 

/I.   III.        H. 

9  30    8.  5 
30  51.  5 
31  33.6 
33     5.  0 
33  47.  1 
34  29.4 

M   15     0.0 
+          2  13.6 

2  45  49.  4 

84  45    0.0 
+          2  31.  1 

9  32  19.2 

o 
Ther.     62.  5 

in. 
Bar.      29.  82 

0      /        /; 

=  73  40  12.  6 

I/,  in.     «. 
.       8  22    3.  1 

+       5  28  4 

O        '           '/ 

=  73  44  59.4 

/I.  111.       S. 

3    8  36.0 
_j_      5  "fi  2 

74  17  13.6 
1  13.3 

+               6.  8 

84  47  31.  1 

59.  5 
+               6.3 

i'nlar  distance  of  ( 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Chrouoin 

Chronometer  fast 

» 
. 

The.se  observatio 

llljeet 

me 

Polar  disfaiiec  ul' 

Local  Apparent  Ti 
Equation  of  Time 

Local  Mean  Time 
Time  by  Clironom 

Chronometer  last 
These  observatioi 

>hject 
me 

8  27  31  5 

3  14    22 

eter    .     .     . 
of  Local  M.  T. 

.      2  45  49.  4 

« 
itcr    . 

if  Local  M.  T. 

.       9  32  19.2 

.       0  18  17.9 

.       6  18  17.0 

is  were  made  before  noon. 

is  were  made  after  noon. 

11* 


82 


REPORT    OF   PROFESSOR    HARKNESS. 


SCHEDULE  A— Continued. 


SUN              '„        .        .        AUGUST  7. 

SUN       ....        AUGUST  8. 

Index  Covr. 
E 

Index  ('CUT.,  &<•. 

On  Are  =  u.      Off  Arc  =  w1. 

(Mi  Arc  =  u. 

Off  Arc=<A 

i 
/      //                  c      i      a 

/     // 
•«)  :in 
:, 

; 

Q         1           II 

•\  26     5 

to 

10 

+          2  15.0 
+               15.4 

Index  Corr.              +           2  10.  8 
E                              +              17.  8 

•f          2  30.4 

Index  Ci.n-..  Ac.     +           2  28.6 

Means 
Index  Con1.,  &c. 

Q 

Refraetion 
Parallax 

2  Altitude.       Chronometer. 

2  Altitude. 

Chronometer. 

A.  m.     s. 
82    (I    (I              9  38  32.  8 

PI  45   (i              39  14.  r. 

30     (1                   39  50.  5 
82     0     0                   41  28.0 
PI  45     0                   42     8.8 
:!0     0                   42  50.7 

0        /        " 

91   30     0 
45     0 
92     0     0 
91  30     0 
45     0 
92     0    0 

A.    HI.       S. 

::  33  33.  0 
34  16.5 
35     0.5 
36  36.  5 
37  20.0 
38    4.2 

81    15     0.0           9  40  41.9 

Means                             111  45     0.0 
Index  Corr.,  &c.    +          2  28.  6 

3  35   1-.  1 

+          2  30.  4 

o 
Ther.    69.5 

i». 
Bar.       29.75 

0        '          " 

-  73  57  50.  :: 

A.     »«.        K. 

9  12  10.9 
+       5  20.  6 

81  47  30.4     Ther.    74. 

1    9'7         - 
+               C>.4     Bar.      29.76 

U                                    91  47  28.6 
Refraction                               53.  0 
Parallax                  +               5.  9 

Polar  distance  of 

Local  Apparent  T 
Equation  of  Time 

Local  Mean  Time 
Time  by  Clironom 

Chronometer  fast 
These  oliservatio 

o      /       /' 
object                    -  73  45     5.3 

A.  ?».      s. 
me                               3  16  58  7 

Polar  distance  of  object 

Local  Apparent  Time 

'.  +       5  26.2 

Local  Mean  Time       .... 

Time  liy  Chronometer     . 

Chronometer  fast  of  Local  M.  1> 

3  22  24  9 

9  17  31.5 
3  35  48.  4 

eter     .  .                     9  40  41.9 

of  Loenl  M.T.   .       C.  18  17.0 

.       6  18  16.9 

us  were  made  after  noon. 

These  observations  were  made  before  noon. 

OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST    7,    JSG'J. 
SCHEDULE  A— Continued. 


SUN 


AUGUST  8. 


On  Arc  =  u.      Oft'  Arc 


29  25 
30 
30 


Index  Corr. 
E 


2  15.0 
11.4 


Index  Con-.,  &c.    !+          2  26. 4 


2  Altitude. 


Means 

Index  Con'.,  &c. 

£> 

IvYIVactioll 
Parallax 


65  45  0 

30  0 

15  0 

65  45  0 

30  0 

15  0 


65  30    0. 0 
+          2  26.  4 

65  32  26.  4 
1  23.0 

+  '  7.2 


4  26     0 
5 

0 


Chronometer. 


It.    lit.       8. 

10  21  93.3 

22  33.  2 

23  M.5 

24  43.3 

25  23.  5 

26  3.5 


10  23  58.  6 


Thcr.    7(1. 0 

in. 
Bar.      2'J.  64 


1'oliir  distance  of  object 

Local  Apparent  Time 

Equation  of  Time 

Local  Mean  Time       .     . 
Time  by  Chronometer 


=    74    2  42.0 

h.  in.    y. 
.       4     0  23. 1 

.   +       5  18.3 


4     5  41.4 

10  23  58. 6 


Chronometer  fast  of  Local  31.  T.   .       6  18  17. 2 


These  observations  were  mudo  after  noon. 


83 


84 


REPORT    OF    PROFESSOR    HARKNESS. 


SCHEDULE  13. 

Observations  for  Latitude,  made  at  the  temporary  United  States  Naval  Observatory  at  Des  Moines, 
Jozra,  by  Prof.  Wm.  Harkn»8S,  U.  S.  N.,  icith  the  /Sextant  M«clq>ole.  A-  Bro.  No.  0,'!7. 
Artificial  Horizon  Ha.  1,  and  Chronometer  T.  >S'.  &  J.  I).  Negus  No. 


[NOTE.  —  Tlic  barometer  employed  was  an  aneroid  belonging  to  Professor  J.  E.  Eastman,  and  O.MS  of  an  inch  must 
be  subtracted  from  all  its  recorded  readings  in  order  tn  free  them  from  constant  errors.] 


SUN        .         .                 JULY  23,  1869. 

SUN                  .         .  '      JULY  23,  1869. 

Index  Corr. 
E 
Art.  Hor. 

Index  Con-.,  &c. 

On  Arc  =  u. 

Off  Are  =u'. 

Index  Corr. 
E 
Art.  Hor. 

Index  Corr.,  &c. 

On  Arc  =  a. 

Off  Arc  =  o'. 

i     n 
28  30 
30 
20 

O        /         " 

4  26  20 
10 
0 

i       tf 

0       /        /' 

+          2  41.6 
+              29.6 

-f         241.6 
+              29.8 

+          3  11.2 

+         3  11.4 

Means 
Index  Corr.,  &c. 

H 

f 

Refraction 

Parallax 
Am0 
Bnc 

ft' 

9 

2  Altitude. 

Chronometer. 

Means 

Index  Corr.,  &c. 

S2 

? 
Refraction 

Parallax 
Am0 
Bn0 

6 

<t> 

2  Altitude. 

Chronometer. 

O         '       " 

136  15  30 

•2(1  30 
24  40 
135  27  20 
31  40 
35  40 

7(.     JH.      8. 

6    2    7.0 
3  10.8 
3  55.  3 
4  58.5 
5  58.2 
6  56.8 

0          '        " 

135  58  10 
136    0  30 
2    0 
U!7    7    0 
9    0 
10  50 

A.  in.     «. 
(i  13  20.  8 
14  14.2 
14  45.0 
15  57.  5 
16  59.  3 
17  59.0 

135  55  53.  3 
+          3  11.2 

6    4  31.  1 

136  34  35.  0 
+          3  11.4 

6  r5  32.  6 

o 
Thcr. 

in. 
Bar. 

7i.    HI.     s. 
=  12    6  10.  9 

(i  1H     8.0 

o 
Ther.      86.  5 

/I.      Ml        8. 

=  12    6  10.  9  ' 

=     6  18    8.0 

135  59    4.  5 

136  37  46.  4 

22    0  27.  8 
-f-              21.  7 
3.2 
—        24  38.4 

+               13.8 

21  41    6.6 
+              21.  4 
3.1 

—       -i  58.  :: 

21  3fi  *J. 
+  19  59    3. 

21  36  27. 

-f  19  58  57. 

•H  ;;r,  •,'.-. 

41  35  24. 

Time  of  Culmination      .     .     - 
Chronometer  fast       .... 

Chron.  Time  of  Culmination     . 

Time  of  Culmination      .      .      . 
Chronometer  fast       .... 

Chron.  Time  of  Culmination 

=    6  24  18.  9 

=     (i  24  18.  9 

OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST    7,    1869. 


85 


SCHEDULE  B— Continued. 


SUN                                              JULY  24. 

SUN           ....        JULY  25. 

Index  Con. 
E 
Art.  Hor. 

Index  Corr.,  &c. 

On  Arc  =  a. 

Off  Arc  =  u'. 

Index  Corr. 
E 
Art.  Hor. 

Index  Corr.,  &c. 

On  Arc  =  a. 

Off  Arc  =  u>. 

i      a 
29    5 
10 
10 

0       /        II 

1  26    0 

20 
10 

t      i/ 
29  25 
30 
30 

Q        1          it 

\  20  10 
25  55 
50 

+          2  20.  8 
+             29.7 

+          2  16.7 
+             29.6 

+          2  50.  5 

+          2  46.  3 

Mean.-. 
Index  Corr.,  Ac. 

a 

i 
Refraction 
Parallax 
Am0 
Bn0 

i 
* 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 

a 

c 

Refraction 

Parallax 
AmQ 
Bn0 

i 
9 

2  Altitude 

Chronometer. 

0          '        " 

136  17  45 
20  10 
22  20 
135  23  10 
25  10 
29  30 

7l.        111.           X: 

6    7  51.5 

8  32.  0 
9    9.  5 

10  11.:; 
10  55.  3 
12    7.0 

Q            i         II 

136  14  40 

23  10 
23  30 
135  21    0 
21  40 
21  10 

h.   m.     s. 
6  15  16.2 
19    5.  1 
21    3.  5 
22  10.6 
23  11.5 
20  43.  5 

135  53    0.8 
+          2  50.  5 

6    9  47.  H 

135  50  51.7 
-f          2  46.  3 

6  21   15.  1 

0 

Ther.      86.  0 

/(.      HI.       H. 

12     6  12.0 
=     6  18    8.5 

o 
Ther.     71.  5 

in. 
Bar.      29.  48 

h.    m.     s. 
=  12    6  12.6 

=     6  18    8.9 

135  55  51.  3 

i::r,  :,:;  ::.«.o 

22    2    4.4 

+             21.7 
3.2 
13  14.5 
+                4.0 

22    3  11.0 
+             22.4 
3.2 
1  21.9 

21  49  12. 
+  19  46  24. 

22    2    8. 
+  19  33  21. 

41  35  36. 

41  35  29. 

Time  of  Culmination 
Chronometer  last        .... 

Chron.  Time  of  Culmination    - 

Time  of  Culmination 
Chronometer  fast      .... 

Chron.  Time  of  Culmination    . 

=     6  24  20.  5 

=    6  24  21.5 

86 


REPORT    OF   PROFExSSOR    HARKNESS. 


SCHEDULE  B— Continued. 


SUN          ....        JULY  26. 

SUN                    .         .         .        JULY  27. 

Index  Corr. 
E 
Art.  Hor. 

Index  Corr.,  &c. 

On  Arc  =  u. 

Off  Arc  =  u'. 

Index  Corr. 
E 
Art.  Hor. 

Index  Corr.,  &c. 

On  Arc  =  u. 

(Ill  Arc  =  u'. 

29  15 

28  55 
50 

O      /          If 

4  26  10 
40 
10 

/     n 
29  10 
25 
25 

O      '         " 

4  26     0 
26     0 
25  50 

+          2  20.  0 
+              29.5 

+          2  21.  6 
+              29.  4 

4-        2  49.  5 

4-          2  51.  0 

Means 
Index  Corr.,  &c. 

Q 

f 
Refraction 

Parallax 
Am-,      ' 

f, 

2  Altitude. 

Chronometer. 

.Means 
Index  Corr.,  &c. 

a 

Refraction 

I'arallax 

<5 

2  Altitude. 

Chronometer. 

0        '        II       • 

135  36  50 

57  50 
57  45 
134  55    0 
55  20 
54  40 

/i.  m.     s. 
6  21     8.  5 
22    2.8 
22  40.  7 
23  39.2 
24  13.8 
24  41.5 

o      '      " 
134  25  10 
23  50 
22  40 
135  24  40 
24     0 
22  40 

//.   HI.       S. 

6  29  27.  5 

:;o    9.7 

30  48.7 
31  34.5 
32  I'.'.'.i 
:«  52.2 

135  26  14.  2 
4-          2  49.5 

6  23    4.  4 

134  53  50.  0 
+          251.0 

6  31  12.  0 

0 

Ther.    79.0 

I'M. 
Bar.      29.  51 

/I.      Ml.      8. 

=  12    6  12.6 

=    6  18    9.4 

0 

Ther.     80.3 

in. 
Bar.      29.  46 

/I.     Ml.       S. 

=  12    6  12.1 

=    6  18  10.  4 

135  29    3.7 

134  5<;   IK" 

22  15  28.  2 
4-              22.4 
3.2 
11.7 

22  31  39.  5 
4-              22.5 
—               3.  2 

2  54.  8 

22  15  36. 

4-  19  20    4. 

22  29    4. 
4-19    6  25. 

41  35  40. 

41  35  29. 

Time  of  Culmination      .     .     . 
Chronometer  fast       -     -     - 

Chrou.  Time  of  Culmination 

Time  of  Culmination      .     .     . 
Chronometer  fast       .     -     -     - 

Chron.  Time  of  Culmination     . 

=    6  24  22.  0 

=    6  24  22.  5 

OBSERVATIONS    OF   THE    ECLIPSE    OF   AUGUST   7,    18C9. 


87 


SCHEDULE  B— Continued. 


SUN        .        .        .        .        JULY  28. 

SUN        ....        JULY  28. 

Index  Corr. 
E 
Art.  Hnr. 

Index  Corr.,  &c. 

On  Arc  =  o 

Off  Are  =  ul 

Index  Corr. 
E 
Art.  Hor. 

Index  Corr.,  &c. 

On  Arc  =  u 

Off  Are  =  u1 

/     // 
28  50 
20    0 
29    0 

o    /      // 
4  25  50 
26  10 
26  10 

i    n 

O      '       " 

+          2  30.0 
+             29.3 
0.3 

-f      2  30.  0 
+          29.3 

+            0.3 

+          2  59.  0 

+      2  59.  6 

Means 

Index  COIT.,  &.c. 

a 

f 

Refraction 
Parallax 

.tnl 

Iin0 

6 
* 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 

a 

f 
Refraction 
Parallax 
Ams 
B*o 

f 

$ 

2  Altitude. 

Chronometer. 

0        /        II 

135    o  no 
2   r, 

2  25 
133  59  50 
59  30 
59  40 

It.  HI.     s. 
6  20  11.  0 
21    7.5 
21  50.0 
22  40.  0 
23  13.0 
23  42.5 

o      /      '/ 
133  59  30 
134     0    0 
133  59  40 
135    2  35 
1  30 
1  20 

It.  in.    s. 
C,  25    8.  0 
25  43.2 
26  15.8 
26  59.5 
27  50.  5 
28  29.  2 

134  :«J  43.3 
+        .  2  59.  0 

6  22    7.3 

134  30  45.  8 
+          2  59.  6 

6  26  44.  4 

/I.      lit.      S. 

=  12    6  10.9 
=     6  18  11.5 

o 
Ther.    71. 
in. 
Bar.       29.  59 

/i.    HI.    ». 
=  12    6  10.9 

=     6  18  11.5 

134  33  42.  3 

134  33  45.4 

22  43    8.8 
+             23.1 
3.2 
23.1 

22  43    7.  3 
+             23.1 
3.2 
25.5 

22  43    6. 

+  18  52  36; 

22  43    2. 

+  18  52  33. 

41  35  42. 

41  35  35. 

Time  of  Culmination      .      .      . 
Chronometer  Cast       .... 

Chrnn.  Time  of  Culmination    . 

Time  of  Culmination      .      .      . 
Chronometer  fast      .... 

Cliron.  Time  of  Culmination    . 

=    6  24  22.  4 

=     6  24  22.  4 

REPORT   OP  PROFESSOR   IIARKNESS. 


SCHEDULE   B.— Continued. 


SUN          ....        JULY  29. 

SUN           .         .         .         .        JULY  29. 

Index  Corr. 
E 
Art,  Hor. 

Index  Corr.,  &c. 

On  Arc  =  u. 

Off  Arc  =  u'. 

Index  Corr. 
E 
Art.  Hor. 

Index  Corr.,  &c. 

On  Are  =  o. 

Off  Arc  =  o'. 

i     a 

Ct       t        11 

-/     // 
28  40 
50 
40 

Q     i       it 

4  25  50 
26    0 
20    0 

+          2  40.0 
+              29.1 
+               0.3 

+      2  40.  0 
+          29.1 
(1.3 

+          3    9.4 

+      3    8.8 

Means 
Index  Corr.,  &c. 

0 

f 

Refraction 
Parallax 
Am0 
Bn0 

f, 

fi 

<i> 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 

a 

f 

Refraction 
Parallax 
Am0 
B»0 

6 
0 

2  Altitude. 

Chronometer. 

o       /     // 
134  34  10 
34  35 
34  30 
133  31  30 
31  25 
31  20 

/i.  m.     s. 
0  22  12.  1 
22  56.7 
23  30.6 
24  17.0 
24  49.2 
25  19.5 

O         in 

l:i:i  31  10 
:ui    n 
29  50 
134  32  20 
31  40 
31     0 

//.    HI.        S. 

0  26  46.  0 
27  35.0 
27  59.0 
28  44.0 
29  24.  0 
29  54.  6 

Kit    2  55.0 
+       '  3    9.4 

6  23  50.  8 

134    1    0.  0 

+          3    8.8 

6  28  23.  8 

7i.    m.     s. 
=  12    fi    9.2 

=    C  18  12.0 

o 
Ther.    74.5 

in. 
Mar.       29.66 

/i.    m.     s. 
=  12    0    9.2 

=    6  18  12.0 

134    6    4.4 

134    4    8.8 

22  56  57.  8 
+              23.0 
3.3 

0.1 

22  57  55.6 
+              23.0 
3.  3 
1     2.3 

22  57  12. 

+  18  38  23. 

22  57  13. 

+  18  38  20. 

41  35  35. 

41  35  33. 

Time  of  Culmination      . 
Chronometer  fast       .           .     . 

Chron.  Time  of  Culmination    . 

Time  of  Culmination 
Chronometer  fast 

Chron.  Time  of  Culmination     . 

=    6  24  21.2 

=    6  24  21.  2 

OBSERVATIONS    OF   THE   ECLIPSE    OP   AUGUST   7,    1869. 


89 


SCHEDULE  B— Continued. 


a  AQUILjE       -         -         .         JULY  29. 

POLARIS          .        .        .        JULY  29. 

Index  Corr. 
E 
Art.  Hor. 

Index  Corr.,  &r. 

Coincidence 
of  Images. 

Off  Arc  =  u>. 

Index  Corr. 
E 
Art.  Hor. 

Index.  Corr.,&c. 

Coincidence 
of  Images. 

Off  Arc  =  <A 

/    // 
2  25 
30 
25 

O      '        " 

/     // 

0       /        " 

+          2  26.7 
+             23.6 

+          2  2C.  7 
4-              15.8 

+          2  50.  3 

+          2  42.5 

Means 
Index  Corr.,  &c. 

Q 

c 

Refraction 
Parallax 

Am  > 

Alg 

{, 

6 

<t> 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 
Q 

4H 
Refraction 
p  cos  t 
2d  term 

# 

2  Altitude. 

Chronometer. 

o      /      // 

m  40  20 

47  50 
49  10 
49  15 
49  50 
50  10 

li.  in.    ft. 
5  24  20.  0 
25  34.2 
26  37.0 
27  28.5 
23  12.4 
28  57.5 

0       /        '/ 

83  3-1  111 
34  35 
35  40 
36  10 
36  45 
37  20 

/(.  m.     «. 
5  32  53.  5 
33.  53.  0 
34  42.5 
35  35.  3 
36  23.  0 
37  15.  5 

113  48  45.  H 
+          2  50.3 

H3  35  46.7 
+          2  42.  5 

5  35    7.1 

o 
Ther.    59.  5 

ill. 

Bar.       29.  70 

li.  m.    s. 

0 

Ther.    59.5 

IH. 

Bar.      29.  70 

It.  m.    s. 
6  18  12.  1 

5  23    2  2 

113  51  30.  1 

83  38  29.  2 

33    4  12.0 

+              30.  6 

53.  3 

41  49  14.  C 

1     3.0 
13  25.  4 
+              53.1 

41  35  39. 

33    3  55. 

+     8  31  42. 

Chronometer  fant      .... 
t 

41  35  37. 

Time  of  Culmination       .      .      . 
Chronometer  fast  

Chrou.  Time  of  Culmination    . 

6 

)-  88°  36'  25" 
5015" 

=  11  12  51.9 
=    6  18  12.  1 

P  - 

=    5  31    4.  0 

12* 


90 


REPORT    OF   PROFESSOR   HARKNESS. 


SCHEDULE  B— Continued. 


SUN          ....        JULY  30. 

SUN          ....        JULY  30. 

Index  Corr. 
E 
Art.  Ilor. 

Index  Corr.,  &e. 

On  Arc  =  w. 

Off  Arc  =  u'. 

Index  Corr. 
E 
Art  Hor. 

Index  Con-.,  &c. 

On  Arc  =  a. 

Off  Arc  =  o1. 

/     // 
29  10 
10 
15 

O       '          H 

4  26    5 
10 
20 

i    n 

o     '     " 

+          2  18.3 
+              29.0 
0.3 

+          2  18.3 
+              29.0 
+               0.3 

+          2  47.0 

+          2  47.  6 

If  •MM 

Index  Corr.,  &c. 

a 

C 

Refract  inn 
Parallax 
Am0 
7?»0 

ti 

a 

0 

2  Altitude. 

Chronometer. 

Means 
Index  Corr..  iVi  . 

Q 

f 
KY  Tract  ion 
Parallax 
Am  o 
Bns 

C, 

<5 
t 

2  Altitude. 

Chronometer. 

O            III 

134    5  10 
r>  45 

5  45 
133    2  40 
3     0 

2  :io 

7l.  Ml.        ». 

6  21  47.  3 
22  18.2 
22  54.0 
23  24.  5 
24  19.2 
24  50.8 

c        /     " 
133    2  30 
2  25 
2    5 
134     4  50 
4  20 
4  15 

/I.   Ml.        S. 

0  26    3.  5 
20  32.2 
20  51.2 
27  21.8 
27  50.8 
28    7.5 

133  34     8.  3 
+          2  47.  0 

6  23  15.  7 

i:;:i  33  24.2 

+          2  47.  6 

C  27    7.8 

/I.      Ml.        S. 

-  12    f.    0.9 
-    6  18  12.2 

o 
Ther.     79.6 

in. 
Bar.      29.  65 

7l.     Ml.        «. 

-  12    6    6.9 
:    C  18  12.2 

133  30  55.  3 

133  Itf.  11.8 

23  11  32.4 
+              23.0 
3.3 

8.  1 

23  11  54.  1 

+              23.  0 
3.3 
29.7 

23  11  44. 

+  18  23  52. 

23  11  44. 

+  18  23  50. 

41  35  36. 

41  35  34. 

Time  of  Cnlmiuation      .     .     . 
Curonometer  fast       .      . 

Chron.  Time  of  Culmination    . 

Time  of  Culmination 
Chronometer  fast      ... 

Chron.  Time  of  Cnlmiuation    . 

=    6  24  19.  1 

=    6  24  19.  1 

OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST   7,    1869. 


91 


SCIIKW.'LK  B— Continued. 


POLARIS                                     .11  'LY  30. 

SUN                             -         -        JULY  31. 

Index  ('CUT 
E 
Art.  Hc.r. 

Index  Corr.,  &c. 

Coincidence 
of  Images. 

Oft  Arc  —  u'. 

Index  Corr. 
E 
Art.  Hor. 

Index  Corr.,  &c. 

On  Arc  =  a. 

Off  Arc  =  u'. 

/    // 
2  20 
15 
25 

O        f       I/ 

t     a 

29  10 

5 

20 

o     /       // 
4  26     0 
25  55 
26    5 

4          2  20.  0 
4-               15.9 

4-          2  24.  2 

+             28.  9 
0.3 

4-          2  35.  9 

+          2  52.  8 

Means 

Index  Corr.,  Ac. 

a 

4  a 
Refraction 

p  r<>;-  / 

ad  term 
* 

•>  Altitude. 

Chronometer. 

Means 
Index  Con1.,  &e. 

Q 

? 
Refraction 
Parallax 
Amo 
Bn0 

ct 

lJl 

0 

2  Altitude. 

Chronometer. 

O       '        II 

83  53  20 
54  10 
55    0 
56    0 
57  10 
57  55 

/I.    III.       S. 

5  55  25.  1 
56  43.6 
57  22.5 
58  47.  2 
6    0  46.2 
2    6.5 

o      /       " 
133  35     0 
35  25 
35  35 
132  33     0 
33  10 
33  10 

/I.  Ml.       8. 

6  21  27.  a 
22  10.8 
22  50.  5 
23  25.  8 
24    4.  3 
24  31.8 

83  55  35.  8 
4-          2  35.9 

5  58  31.  8 

133    4  13  3 

+          2  52.  8 

6  23    5.  1 

O 

Ther.    63.0 

in. 
Bar.       29.117 

o 
Ther.     81.  5 

in. 
Bar.      29.  02 

/I.    III.        S. 

=  12    6    3.9 
=    6  18  13.6 

83  58  11.7 

133    7    6.1 

41  59    5.8 
1     1.4 
—        23    9.0 

4-             50.  6 

23  26  27.  0 
+             23.2 
3.4 

9.1 

41  35  46. 

,  23  26  38. 
4-  18    9    3. 

7l.  III.     8. 

Chronometer  fast       ....            6  18  12.  9 
t        4  55  40.7 
6        +88°  36'  25".  3 
p       5014".  7 

41  35  41. 

Time  of  Culmination      .     .     . 
Chronometer  fast       .... 

Chroii.  Time  of  Culmination    . 

-^    6  24  17.  5 

92 


REPORT   OF   PROFESSOR    HARKNESS. 


SCHEDULE  B— Continued. 


SUN          ....        JULY  31. 

SUN      ....        AUGUST  2. 

ludex  Corp. 
E 
Art.  Hor. 

Index  Corr.,  &c. 

On  Arc  =  a. 

Off  Arc  =  u'. 

Index  Corr. 
E 
Art.  Hor. 

Index  Con-.,  &c. 

On  Arc  =  a. 

Off  Arc  —  u1. 

o     /      // 

/    n 
29  40 
30 
30 

0      '       II 

4  26  25 
20 
30 

+          2  24.  2 

+             28.8 
+               0.3 

+          2    0.8 
+              28.6 
+               0.3 

+       a  53.3 

+          2  29.7 

Means 
Index  Corr.,  &c. 

0 

f 
Refraction 
Parallax 
Am0 
Bn0 

i 

0 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 

Q 

f 

Refraction 
Parallax 

^»»o 
Bn0 

6 

4> 

2  Altitude. 

Chronometer. 

o      /     // 
133  33  20 
32  45 
32  20 
132  29    5 
28    5 
26  55 

/I.   HI.      8. 

6  28  50.  2 
29  24.0 
29  53.  0 
30  20.  5 
30  54.  0 
31  17.5 

Q           1        II 

132  34  40 
33  35 
33    0 
131  29  10 

28  50 

28  15 

/I.  »l.      8. 

6  26  38.  5 
27  53.2 
28  40.2 
29  13.8 
29  38.9 

30    1.5 

133    0  25.  0 
+          2  53.  3 

6  30    6.  5 

132    1  15.0 
+          2  29'.  7 

6  28  41.  0 

• 

7l.      »«.        8. 

=  12    6    3.9 
=    6  18  13.6 

o 
Th,T.      81. 

in. 
Bar.      29.58 

It.      111.      8. 

=  12    5  56.  4 
=    6  18  14.5 

133    3  18.3 

132    3  44.7 

23  28  20.  8 
+              23.2 
3.4 
2    0.1 

23  58    7.7 
+             23.7 
3.5 
1  M.2 

23  26  41. 

+  18    8  58. 

23  57  14. 
+  17  38  27. 

41  35  39. 

41  35  41. 

Time  of  Culmination      .     .     . 
Chronometer  fast       .... 

Chrou.  Time  of  Culmination    . 

Time  of  Culmination 
Chronometer  fast       .... 

Chron.  Time  of  Culmination    . 

=    6  24  17.  5 

=    6  24  10.9 

OBSERVATIONS    OF   THE    ECLIPSE    OF    AUGUST    7,    1869. 


93 


•SCHEDULE  B— Continued. 


SUN      ,        .        .                AUGUST  2. 

a  OPHIUCHI                  .        AUGUST  2. 

Index  Corr. 
E 
Art.  Hor. 

Index  Corr.,  &e. 

(In  Arc 

Oft"  Arc  =  u'.* 

Index  Corr. 
E 
Art.  Hor. 

ludex  Corr.,  &c. 

Coincidence 
of  Images. 

Off  Arc  =  u1. 

i     it 

/      // 

i 

/    // 
2  15 
15 
25 

of" 

+          2    0.8 
+             28.5 

0.3 

+          2  18.3 
4-              25.9 

4-          2  29.  0 

+          2  44.2 

Means 
Index  Corr.,.&-c. 

Q 

^ 
Refraction 
Parallax 
Ama 

fin 

6 
t 

•>  Altitude. 

Chronometer. 

Means 

Index  Corr.,  Ac. 

a 

f 

Refraction 
Parallax 
Am0 
Sii0 

6 

4 

2  Altitude. 

Chronometer. 

o      /       /. 

132  20   n 

25     n 

•_•:;  :;:> 

131  19  20 

17  .in 

15  45 

A.  in.     *. 
(i  33  10.  0 
33  35.  0 
34  11.5 
34  4y.O 
35  24.  0 
36     1.4 

o       /    // 
122    5  50 
4  40 
4  50 
3  30 

a  50 

2  30 

h.  m.    8. 
3    a  30.  1 
341.  5 
4  40.2 
5  44.  0 
6  24.  0 
6  59.5 

131  51  13.3 

+        a  ay.  o 

6  34  31.8 

122    4    1.7 
+          2  44.2 

3    4  59.9 

It.     Hi.      «. 

=  12    5  56.  4 
=    6  18  14.5 

0 

Ther.    74.0 

in.  • 
Bar.      29.  61 

A.  m.    s. 
=    8  41  57.  8 

=    6  18  14.6 

131  53  42.3 

122    6  45.  9 

24    3    8.  8 
+              23.8 
3.5 
<i  12.  0 

28  56  37.  1 
+             29.9 

1  15.4 

23  57  17. 
+  17  38  24. 

28  55  52. 
+  12  39  41. 

41  35  41. 

41  35  33. 

Time  of  Culmination      .... 
Chronometer  fast       -     .     .     .     : 

Chron.  Time  of  Culmination    .    - 

Time  of  Culmination      .      .      . 
Chronometer  fast                     .    - 

Chron.  Time  of  Culmination    . 

=    6  24  10.  9 

=    3    0  12.4 

94 


EEPORT   OF   PROFESSOR   HARKNESS. 


SCHEDULE  B— Continued. 


POLARIS      .        -        .        AUGUST  2. 

a  AQUIL*  .         .         .         AUGUST  2. 

Index  Corr. 
E 
Art.  Hor. 

Index  Corr.,  &c. 

Means 
Index  Corr.,  &c. 

Q 

ta 

Refraction 
p  cos  / 
2d  term 

<t> 

Coincidence 
of  Images. 

Off  Arc  =  <a'. 

• 

Index  Corr. 
E 
Art.  Hor. 

Index  Corr.,&c. 

Coincidence 
of  Images. 

Off  Arc  .=  u'. 

/    // 
2  25 
20 
15 

o     '     /' 

/    // 
2  25 
20 
15 

O       1        If        . 

+          2  20.  0 
-r             15.8 

+          2  20.  0 
+              23.5 

+         2  35.  8 

+          2  43.5 

2  Altitude. 

Chronometer. 

Means 
Index  Corr.,  &c. 

0 

f 

Refraction 
Parallax 
Am0 
7?n0 

6 

" 

2  Altitude. 

Chronometer. 

0       /        II 

83  30  20 
31     0 
31  40 
32  45 
32  30 
33  30 

li.  m.     a. 
5  12    5.2 
13  35.4 
14  23.  8 
15  13.5 
16    2.0 
16  48.  0 

0         '        'I 

113  42  45 
41  20 

39  20 
:!?  i:. 
35  10 
32  30 

/I.   HI.       S. 

5  25  16.  5 

26  17.8 
27     9.2 
28  19.  1 
29  .  8.  3 
30    6.8 

83  31  57.5 
+          2  35.  8 

5  14  49.0 

113  38    3.3 
+          2  43.5 

o 
Ther.    69.5 

in. 
Bar.      29.  63 

h.  m.    s. 
6  18  14.7 

5  27  45.  6 
h  88°  36'  25".9 
5014".! 

o 
Ther.    69.  5 

in. 
Bar.    29.  63 

7l.    Ml.         8. 

=  10  57    8.  3 
=    6  18  14.6 

83  34  33.  3 

113  40  46.8 

41  47  16.6 
1     1.0 
11  43.0 
+             53.4 

33    9  36.  6 
+              35.7 

(i  5:i.  7 
+               0.7 

41  35  26. 

33    3  19. 
+    8  31  42. 

Chronometer  fast       .... 
1        
6        .     .     .  - 

9 

41  35     1. 

Time  of  Culmination      .     .     . 
Chronometer  fast       .... 

Chron.  Time  of  Culmination    . 

=    5  15  22.  9 

OBSERVATIONS   OF   THE   ECLIPSE    OF   AUGUST   7,    1809. 


95 


SCHEDULE  B— Continued. 


a  SAGITTARII      .         .        AUGUST  4. 

Index  Coir. 
E 
Art.  Hnr. 

Index  Corr.,  &r. 

Coincidence 
of  Images. 

Off  Arc  =  a'. 

/    a 
2  10 
20 
10 

0       >       II 

+          2  13.3 

+               0.8 

+          2  20.  1 

Means 
Index  C'orr..  Ac. 

a 

f 
Refraction 
Parallax 

-^"'o 
Bit? 

:, 
3 

<t> 

2  Altitude. 

Chronometer. 

O       '          II 

43  40    0 
35  40 
33  50 
33  30 
30    0 
29     0 

//.   HI.       8. 

4  29  34.  5 
30  43.  0 
31  43.5 
32  39.  0 
33  35.0 
34  16.2 

43  33  40.  0 
+          2  20.  1 

o 
Tlier.     77.  U 

h>. 
liar.      29.  46 

/I.  III.       8. 

-    9  52  11.0 
:     fi  18  15.6 

43  36    0.  1 

r,s  1-2   o.o 

+          2  12.8 

11    ;i.  9 

+                0.4 

68    3    3. 
-  20  27  15. 

41  35  48. 

Time  of  Culmination 
Chronometer  fast        .... 

Chron.  Time  of  Culmination    . 

=    4  10  26.  6 

96 


REPORT   OF   PROFESSOR    HARKNESS. 


SCHEDULE  C. 

Observations  for  Time,  made  at  the  United  States  Naval  Observatory,  Wxxhinf/ton,  with  the  East  Transit 

Instrument,  by  Professor  M.  Yarnall,  U.  8.  N. 

[NOTE. — The  seoouds  were  marked  on  the  chronograph  sheet  by  the  Kcssels  clock,  but  the  beginning  of  the  minutes 
was  taken  from  the  face  of  a  counting  clock,  which  ran  quite  irregularly.  This  accounts  for  tin1  discrepancy  between 
the  hourly  rates  and  the  absolute  errors  on  the  different  days.]  ,  • 


Object. 

Seconds  of  transits. 

a 
o  .ti 

s* 

Date. 

si 

,a 

tg  to 
i)  « 

ZZ 

Almanac 

R.Asccnsion. 

il 

g-o 

V. 

a 

I. 

II. 

III. 

IV. 

VI. 

VII. 

VIII 

IX. 

X. 

XI. 

Mean. 

'c& 

5JS 

K 

o 

O~ 

1869. 

8. 

8. 

s. 

R. 

s. 

s. 

8. 

8. 

s. 

s. 

8. 

in.    s. 

s. 

h.  m.     s. 

s. 

July  26 

1 

14  0 

16    1 

17  6 

07  q 

.,,,  <i 

•w  t 

11  6 

•V>  6 

13  0 

44  0 

46  4 

7  30.24 

+        0.48 

11    7    8.16 

—22.  56 

2 

/?  Leouis      .   29.231.3 

32.5 

42.5 

43.5 

44.7 

15.9 

47.0 

57.  0 

58.1 

0.2 

42  44.  "t 

+        0.5o 

11  42  22.67 

—22.55 

3 

6  Ursa?  Min.     .  . 

_ 

. 

33.  5 

52.  0 

26.5 

18  57.  40 

—  3  45.71 

. 

—22.  45 

4 

a  Lyrse  .     .35.3 

37/9 

39/3 

51.  6 

52.9 

54.5 

36/0 

57.  3 

9.7 

11.0 

13.7 

32  54.  47 

+         0.  43 

18  32  32.  45 

—22.  45 

5 

e   Delphini  .     6.  11  8.  3  9.  4 

19.0 

20.2 

21.4 

22.6 

23.  7 

33.4 

34.6 

36.6 

27  21.39 

+         0.  51 

20  26  59.  48 

—22.  42 

6 

li  Aquarii    .  143.946.247.4 

57.1 

58.2 

59.3J  0.6 

1.6 

11.2 

12.4 

14.6 

45  59.  32 

+        0.  57 

20  45  37.47—22.42 

29 

7 

&  Ophiuchi  .    35.  6 

37.938.9 

48.5 

49.6 

50.751.1) 

52.  9 

2.6 

3.7 

5.8 

7  50.74 

+         0.  43 

16    7  30.60 

—20.  57 

8 

3  <1 

*>  7 

6  8 

16  r> 

17  6 

18.  8>20.  0 

''I   0 

30  8 

31  9 

34  0 

30  18.77 

+         0.  46 

16  29  58.  67 

—20.  56 

9 

K  Ophiuchi  . 

47.7 

48.8 

50.051.2 

52.2 

1.9 

3.0 

5.2 

51  55.00 

4.66 

16  51  29.  79 

—20.  55 

10 

t-    I'rsie  Mill. 

3.8 

18/4 

26/8 

37.8 

45.2 

54.8  4.2 

11.3 

22.5 

30.  8  46.  4 

59  54.  73 

—         1.85 

—20.  55 

11 

7   Aqnibi' 

9.1 

11.2 

12.3 

21.9 

23.0 

24.325.5 

26.  5 

36.  3 

37.  4139.  6 

40  24.28 

-f-         0.  38 

19  40     4.15 

—20.  51 

12 

j3  Aquila- 

0.0 

2.1 

3.1 

12.7 

13.8 

15.  0  16.  2 

17.4 

26.9 

28.  0  30.  2 

49  15.04 

-)-         0.40 

l!i  4*  54.93 

—20.  51 

111 

/    1'i-siH  Miu. 

. 

. 

. 

57.0 

57.0 

56.059.0 

51.0 

_ 

. 

56  56.  00 

10.44 

... 

—20.  51 

14 
15 

IT  Caprieorni 
p   Aqnarii    . 

55.8 
42.3 

68.1 

44.5 

59.2 
45.7 

9.1 
55.3 

10.3 
56.4 

11.6:12.8 
57.  6158.  8 

13.9 

59.8 

24.1 
9.5 

25.427.6 
10.712.8 

20  11.63 

45  57.58 

+         0.  50 
-)-        0  46 

20  19  51.62 
20  45  37.  54 

—20.  51 
—20.  50 

30 

16 

l'i  Leonis      .   28.0 

30.2 

31.2 

41.2 

42.2 

43.644.i- 

45.  9 

55.8 

56.9 

59.  1 

42  43.  54 

+         0.  23 

. 

—21.29 

17 

Polaris.8.P.18.0 

6.5 

5.0 

55.  0 

20.  5 

. 

. 

_  . 

.     . 

49    9.  00 

+22  46.21 

. 

—21.  28 

18 

C  Ophiuchi  - 

4.2 

6.4 

7.4 

17.2 

K3 

19.5 

20.7 

21.7 

31.5 

32.6 

34/8 

30  19.48 

+        0.  37 

16  29  58.63 

—21.  22 

19 

a  Opliiut-lii  . 

58.5 

0.7 

1.9 

11.7 

12.8 

14.1 

15.  3 

16.4 

26.2 

27.2 

29.4 

29  14.02 

+         0.  29 

IT  29  53.  10 

-21.  21 

20 

X  Urae  Min. 

. 

. 

55.  5 

49.0 

50.  0  55.  0 

50.  0 

.     . 

.     . 

_     . 

56  51.90 

14.  83 

. 

—21.  18 

21 

a-  Caprieorni 

54.9 

57/058.3 

8.0 

9.1 

10.4  11.6 

12.6 

22.5 

23.  6 

25.8 

11  10.35 

+         0.  3s 

20  10  49.  56 

—21.  17 

22 

TT  Caprieorni 

56.  6 

58.  8i59.  9 

10.0 

11.1 

12.  4  13.  7 

14.8 

25.0 

26.2 

28.4 

20  12.45 

+         0.  41 

20  19  51.  69 

—21.  17 

23 

/;   A(iuarii    . 

43.2 

45.  3  46.  4 

56.1 

57.  2 

58.4 

V.l.  6 

0.6 

10.4 

11.5 

13.6 

45  58.  39 

+         0.  37 

20  45  37.59 

—21.  17 

24 

C  Cygni  .     . 

27.  H 

30.1 

31.4 

42.  5 

41 

1.  ? 

45.  0  46.  5 

47.7 

58.  6 

0.0 

2.5 

7  45.07 

+         0.21 

21     7  24.  12 

—21.  16 

31 

25 

C  Ophiuchi  . 

4.7 

6.9 

8.0 

17.7 

18.7 

20.021.2 

22.  3 

32.  2 

33.  2 

35.  2 

30  20.01 

+        0.44 

16  29  58.  58 

—21.87 

26 

K   O])hiuchi  . 

:!6.  (i 

38.2 

39.  3 

49.0 

50.  0 

5  1.  \!  .V,'.  1 

53.  5 

3.2 

4.4 

6  5 

51  51.25 

+          0.3S 

16  51  29.76 

—21.87 

27 

<•   Ill-mi1  Min. 

4.4 

18.6 

27.1 

38.2 

46.1 

55.0   3.4 

11.7 

23.5 

30.  9 

46.3 

59  55.  02 

—        0.  52 

. 

—21.  86 

28 

a1  HcTculi.s  . 

48.2 

:>().  4 

51.  5 

1.4 

2.6 

3.7 

4.9 

6.0 

16.  0 

17.1 

19.2 

9    3.73 

+         0.  37 

17     8  42.24 

—21.86 

29 

(!    Ursa-  Min. 

35.  5 

51.  0 

11.532.5 

49.7 

.     . 

_     _ 

15  12.  04 

—         1.  75 

. 

-21.  85 

30 

a   Lyra1,  .     . 

51/1 

52.3 

53.  8 

55.  5 

56.9 

.  .  132.6 

35.  9 

37/3 

39.0 

40.  5 

33  15.49 

—      21.27 

18  32  32.38 

—21.  84 

31 

TT  Caprieorni 

57.  0 

59.  5 

0.6 

10.8 

11.7 

13.  0  14.  3 

15.  4 

25.  5 

26.6 

28.9 

20  13.03 

+         0.4? 

20  19  51.  68 

—21.  82 

32 

f    Delphini  .   j  5.  7 

7.8 

9.0 

18.7 

19.8 

21.0J22.2 

23.4 

33.  0 

34.2 

36.2 

27  21.00 

+         0.  38 

20  26  59.  57 

-21.81 

33 

u    Aquarii     . 

43.7 

45.  9 

47.0 

56.7 

57.  8 

59.0    0.2 

1.3 

11.0 

13.1 

14.1 

45  5S.  9s 

+         0.  44 

20  45  37.  61 

—21.  81 

Aug.  7 

34 

ft  Oeininor. 

.  .    18.7 

21.4 

•!•>.  .- 

24.3 

25.7 

38  22.  58 

—      37.  78 

—27.22 

35 

C    Ophiuclii  . 

9/8 

11.9 

13/0 

•22/9 

24.0 

25.  1  -.'6.  3 

27.4 

37.7 

38.2 

40.4 

30  25.  11 

+         0.  (il 

16  29  :,-.  66 

—27.17 

36 

K   Ophiuchi  . 

41.2 

43.  3  44.  4 

54.2 

55.  2 

56.  5  87.  6 

58.  8 

8.4 

9.6 

11.7 

52  56.  45 

+         0.  53 

16  51  29.  -1 

-27.  17 

37 

r    Ursa1.  Min. 

7.7  83.  6(31.9 

42.8 

49.  9 

59.  7 

7.9 

15.  9 

27.  5 

34.  5 

50.  6 

59  59.  27 

—        0.  44 

. 

—27.  17 

38 

a'  Hereulis  . 

53.  3  55.  5:56.  7 

6.5 

7.6 

8.9 

10.  1 

11.3 

21.0 

22.2 

24.  3 

9    8.85 

+         0.  51 

17    8  42.  19 

—27.17 

. 

39 

c!  I 

rs;e  Mill. 

2.  Oi:i7.  5  55.  0 

38.  5 

56.  0 

17.037.0 

55.  5 

37.  5 

56.  5 

29.0 

15  16.50 

—        2.  54 

. 

—27.17 

40 

K    AquilfP 

4.3   6.4   7.5 

17.4 

18.3 

19.620.8 

21.8 

31.7 

32.  6 

34.  5 

30  19.54 

+         0.60 

19  29  52.  98 

—27.  16 

41 

y   Aquihe 

5.3   7.6 

8.7 

28.  5 

29.5 

30.  ,-::•>.  o 

33.  2 

42.9 

43.9 

46.0 

40  30.71! 

+        0.  53 

19  40    4.  13 

—27.16 

42 

e    Delphini  .    10.913.4 

14.1 

23.8 

24.8 

26.  2i27.  5 

•28.  5 

38.2 

39.3 

41.4 

27  26.  16 

+         0.  53 

20  26  59.  54 

—27.15 

43 

ft   Aquarii    . 

48.750.952.0 

1.9 

2.8 

4.0  5.1 

6.2 

16.0 

17.1 

19.1 

46     3.98 

+        0.61 

20  45  37.44 

—22.  15 

T*        4-r* 

Clock 

Hourly 

10.  Good  observation. 

Date. 

correction 

vat,-.' 

n. 

c. 

18.  Good  observation,  through  thick  haze. 

27.  Very  nnsteadv. 

29.  Very  unsteady. 

1809. 

Aug.  7.  Stars  unsteady  throughout  the  night. 

h. 

R. 

s.               s. 

s. 

s. 

r. 

July  20      16.5 

—    22.48 

+     0.014    +  0.48 

-  0.17 

+  0.06 

July  26,  12h.  Image  west,  0.24.    Clamp  east  . 

29      18.  C 

—    20.53 

+     0.014    +  0.51 

-  0.23 

—  0.09 

July  26,    61).  Image  west,  0.25.     Clamp  east. 

30      18.  3 

—    21.20 

-f     0.014          .     . 

—  0.09 

Image  west,  0.45.     Clamp  west. 

11.2 

- 

.  •    .    +  0.35 

—  0.10 

30,211i.  linage  west,  0.36.     Clamp  west. 

16.4 

„     •  „ 

.    -j-  0.43 

—  0.20 

. 

Image  west,  0.15.     Clamp  east. 

31      18.  6 

—    21.84 

+     0.015    +  0.35 

—  0.18 

+  0.06 

31,           Imago  west,  0.10.     Clamp  east. 

Aug.    7      17.3 

—    27.17 

+     0.005    +  0.50 

—  0.  25 

+  0.07 

Ang.    7,  21h.  Image  west,  0.18.    Clamp  east. 

Image  west,  0.41.     Clamp  west. 

REPORT 


PROFESSOR  JOHN   R.   EASTMAN,  U.  S.  N. 


13* 


REPORT    OF    PROFESSOR    J.    R,    EASTMAN,    U.    S.    N. 


UNITED  STATES  NAVAL  OBSERVATORY, 

Wa-sMn-gtoii,  D.  C.,  September  28,  1869. 

Sin:  In  obedience  to  an  order  from  the  honorable  Secretary  of  the  Navy,  dated  June  14, 1869, 
I  have  the  honor  to  submit  to  you  the  following  report  of  my  observations  of  the  solar  eclipse  of 
August  7, 1809,  at  Des  Moines,  Iowa. 

In  company  with  the  other  members  of  the  party,  I  left  Washington  on  the  5th  and  reached 
Des  Moines  on  the  10th  of  July. 

A  site  for  the  temporary  observatory  was  immediately  selected  in  the  northern  portion  of  the 
city,  on  the  north  side  of  Short  street,  between  Second  and  Third  streets;  but,  owing  to  the 
extremely  bad  weather,  tiro  building,  together  with  the  small  inclosure  for  the  protection  of  the 
meteorological  instruments,  was  not  completed  until  July  20. 

The  following  is  a  list  of  the  instruments  taken  from  Washington:  One  telescope  and  stand 
one  actinometer ;  one  photometer ;  one  barometer  (aneroid)  with  attached  thermometer;  one  dry- 
bulb  thermometer;  one  wet-bulb  thermometer;  one  solar  thermometer ;  maximum  and  minimum 
thermometers;  and  three  mean-time  box  chronometers,  (T.  S.  &  J.  D.  Negus,  Nos.  1275,  1.'500,  and 
1319.)  The  telescope  and  chronometers  were  taken  from  the  Observatory,  but  the  other  instruments 
were  my  private  property. 


DESCRIPTION  Ot 

The  Telexe<>i>c. — The  focal  length 
of  this  instrument  is  IS. 5  inches,  and 
the  diameter  of  the  object-glass  is  3.5 
inches.  The.  celestial  eye-piece  has  a 
power  of  50,  and  is  fitted  with  three 
colored  shades  of  red,  green,  and  neu- 
tral-tinted glass.  The  stand  and  the 
equatorial  mounting  were  made  by 
H.  G.  Fit/,  of  New  York,  and,  though 
working  very  badly,  fulfilled  all  the 
conditions  required  on  the  day  of  the 
eclipse. 

The  Actinometer. — This  instru- 
ment is  in  many  respects  similar  to 
the  one  used  by  the  Rev.  G.  C.  Hodg- 
kinson  in  the  Alps  in  1866,' and  was 
made  by  Messrs.  F.  W.  and  It.  King, 
of  Baltimore,  from  sketches  and 
specifications  which  I  furnished  for 
their  guidance.  It  consists  of  a  ther- 
mometer with  a  spherical  bulb  1.75 
inch  in  diameter  and  a  tube  12  inches 
long.  At  a  distance  of  9.25  inches 
from  the  bulb  the  tube  abruptly  ex- 
pands to  a  diameter  of  0.5  inch  for  a 
distance  of  1.6  inch,  and  terminates 
in  a  spheroidal  chamber  0.8  inch  in 
diameter,  from  which  the  air  is  only 
partially  exhausted.  The  interior 
diameter  of  the  small  tube  is  about  0.06  inch. 


INSTRUMENTS. 


The  bulb  is  filled  with  alcohol  colored  with  aniline 


100 


REPORT    OF   PROFESSOR    EASTMAN. 


blue,  and  the  different  portions  of  the  instrument  are  so  adjusted  that  at  a  temperature  of  about 
40°  Fah r.  the  top  of  the  column  is  very  near  the  bottom  of  the  scale  attached  to  the  tube.  An 
ivory  scale,  10  inches  long  and  0.9  inch  wide,  graduated  in  millimeters,  is  attached  to  the  tube,  its 
lower  end  being  one  inch  from  the  bulb.  Below  the  end  of  the  scale  the  tube  passes  through  a 
cork  bung,  perforated  and  split  to  receive  it,  by  which  the  actinometer  is  attached  to  the  brass 
shading-tube  when  in  use. 

In  order  to  avoid  the  usual  difficulties  in  shading  the  actinometer,  a  plain  brass  tube,  14.1i.> 
inches  long  and  2.4  inches  in  diameter,  open  at  both  ends  and  blackened  on' the  inside,  was  adopted, 
as  affording  the  best  facilities  for  passing  the  bulb  from  the  direct  rays  of  the  sun  into  the  shade, 
and  still  presenting  no  additional  obstruction  to  radiation.  In  the  central  section  of  this  tube  it  is 
pierced  with  a  circular  hole  1.8  inch  in  diameter,  from  which  spiings  a  Hanged  shoulder  which 
receives  and  holds  firmly  the  perforated  cork  on  the  actinometer  tube,  while  the  bulb  of  the  ac.ti- 
nometer  projects  so  far  into  the  tube  that  the  sun  can  shine  completely  round  it. 

Two  brass  caps  with  plain  plate-glass  fitted  into  the  ends  are  made  to  screw  into  the  ends  of  the 
brass  tube,  in  order  to  permit  the  free  passage  of  the  sun's  rays,  and  at  the  same  time  prevent  t In- 
action of  currents  of  air. 

At  90°  from  the  center  of  the  aperture  for  the  actinometer  bulb  is  a  screw  to  connect  the  brass 
tube  with  a  socket,  and  a  strong  wood  screw,  (Fig.  1,  a,)  by  which  the  tube  is  attached  to  a  stall'  or 
post  while  in  use. 

In  using  this  instrument,  the  actinometer  is  attached,  by  means  of  the  perforated  cork,  to  tin- 
brass  tube,  which  is  then  so  adjusted  that  the  sun's  rays  fall  directly  on  the  bulb  until  a  sufficient 
quantity  of  liquid  is  driven  into  the  upper  chamber;  when  the  chamber  is  held  lower  than  the  bulb, 
the  column  is  broken  and  allowed  to  fall  to  the  temperature  at  which  the  instrument  is  to  be  worked. 
The  bulb  of  the  instrument  is  again  exposed  to  the  sun,  and  after  an  interval  of  ten  seconds  the 
height  of  the  column  is  noted  on  the  scale  and  recorded  as  the  first  reading.  At  the  end  of  the 
adopted  period  of  exposure  the  height  is  again  read  and  recorded  as  the  second  reading  in  the*«H, 
and  the  tube  is  turned  away  until  the  bulb  is  perfectly  shaded.  After  the  bulb  has  been  in  the 
shade  ten  seconds  the  height  of  the  column  is  noted  and  recorded  as  the  lirsl  reading,  and,  after 
the  same  interval  as  before,  the  height  is  again  read  and  recorded  as  the  second  reading  in  the  slitulc. 
In  the  same  manner  the  number  of  observations  may  be  increased  at  pleasure.  When  the  working 
column  reaches  the  widened  tube,  more  liquid  may  be  expelled,  and  the  observations  continued  as 
before;  or,  if  the  fall  in  the  shade  is  greater  than  the  rise  in  the  sun,  the  column  may  be  expanded 
until  it  reaches  the  widened  tube,  when,  if  it  is  not  broken  and  is  allowed  to  contract,  enough  liquid 
may  be  withdrawn  to  maintain  the  column  at  a  proper  working  height. 

The  temperature 
of  the  liquid  is  de- 
termined from  a  table 
derived  from  com- 
parison with  a  stand- 
ard thermometer  to 
ascertain  the  tem- 
perature of  the  col- 
umn when  it  reaches 
the  following  points, 
viz:  0  on  the  scale, 
the  junction  of  the 
small  and  widened 
tubes,  and  the  vari- 
ous divisions  of  the 
scale  for  the  widened 
t  ube. 

The  Photometer. — 
This  instrument  was 
devised  for  the  pur- 


1869.  101 

pose  of  measuring  the  relative  amount  of  diffused  light  in  the  atmosphere  at  different  periods  in 
the  progress  of  the,  eclipse,  and  was  constructed  from  my  own  designs.  It  consists  of  one  main  tube 
of  brass  10.2  inches  long  and  2,5  inches  in  diameter,  intersected,  at  1.8  inch  from  the  bottom  and 
at  an  angle  of  30°,  by  a  small  brass  tube  8.0  inches  long  and  1.1  inch  in  diameter;  a  brass  plate 
with  a  flange  in  the  center  which  screws  into  the  bottom  of  the  main  tube,  and  an  apparatus  for 
regulating  the  area  of  the  aperture  admitting  the  light,  which  tits  by  a  thin  flange  into  the  upper 
end  of  the  main  tube. 

This  apparatus  (Fig.  2,  <i)  is  inclosed  between  two  brass  [dates  pierced  by  a  hole  of  nearly  the 
diameter  of  the  main  tube,  and  consists  of  two  thin  brass  plates,  each  pierced  by  an  aperture  1.46 
inch  square  to  admit  the  light,  sliding  on  each  other,  by  means  of  a  double  rack  and  pinion  move- 
ment, in  opposite  directions. 

The  reduction  of  the  aperture  admitting  the  light  is  measured  by  the  revolutions  of  a  gradu- 
ated disk  1.5  inch  in  diameter,  attached  to  the  pinion  shaft  and  adjustable  by  means  of  a  binding 
screw.  Upon  the  plate  at  the  bottom  of  the  main  tube  was  fastened  a  disk  of  black  paper,  (Fig.  2, 
6,)  upon  which  was  painted  a  small  live-pointed  star,  the  points  and  center  of  which  were  white;  a 
black  circle  or  ring  was  drawn  through  the  bases  of  the  points,  and  a  small  black  dot  made  in  the 
center  of  the  ring. 

In  using  this  instrument,  it  is  first  lixed  witti  the  main  tube  in  a  vertical  position,  and  a  thin 
plate  of  ground  glass  is  placed  over  the  aperture  admitting  light.  The  eye  is  then  placed  at  the 
end  of  the  small  tube,  lilting  close  enough  lo  shut  out  all  light,  and  the  aperture  is  gradually  dimin- 
ished, by  turning  the  head  of  the  pinion  shaft,  until  the  "ring"  in  the  star  suddenly  disappears. 
The  observer  then  reads  and  records  the  revolutions  of  the  graduated  pinion  head.  Five  readings 
are  sullicient  for  a  good  observation.  The  pinion  head  is  divided  into  100  equal  parts,  and,  as 
one  revolution  effects  a  change  of  0.83 1  inch  in  the  length  of  the  side  of  the  aperture,  one  division 
will  represent  a  change  of  0.1108  inch. 

Aneroid  Bannm-tcr. — This  instrument,  made  by  J.  T.  Large,  is  graduated  to  0.02  inch,  with  a 
range  of  scale  from  27.70  to  .'51. .'JO  inches,  and  is  provided  with  an  attached  thermometer.  Its  errors 
were  determined  by  comparison  with  the  observatory  standard,  before  and  after  the  trip  to  Iowa, 
and  by  comparison  on  the  day  of  the  eclipse  with  an  instrument  owned  by  Mr.  A.  McConuell,  who 
determined  the  errors  of  his  barometer  before  and  after  the  trip  by  comparison  with  the  standard 
at  the  Dearborn  Observatory,  Chicago. 

Thermomclcrx. — The  dry,  wet-bulb,  and  solar  thermometers  were  made  by  James  Green,  and, 
upon  careful  comparison  with  the  observatory  standard,  no  scale  errors  could  be  detected.  The 
solar  thermometer  has  a  blackened  bulb,  and  is  inclosed  in  au  exhausted  glass  tube. 

The  maximum  and  minimum  thermometers  were  made  by  F.  W.  &  E.  King.  They  are  mounted 
side  by  side  on  the  same  plate,  and  by  comparison  the  errors  were  ascertained  to  be  less  than  the 
probable  error  of  a  single  reading. 

The  Chronometers  were  of  the  common  style,  made  by  T.  S.  &  J.  I).  Negus  for  the  use  of  the 
navy,  and  were  selected  for  this  service  on  account  of  the  steady  rates  which  they  had  maintained 
for  several  months. 

The  meteorological  instruments  were  placed  in  a  small  inclosure,  sixteen  feet  square,  about 
seven  yards  southeast  from  the  temporary  observatory. 

The  barometer  and  the  dry  and  wet  bulb  and  maximum  and  minimum  thermometers  were 
placed  in  a  box  18  inches  long,  12  inches  wide,  and  15  inches  high,  made  on  the  east,  south,  and 
west  sides  of  two  thicknesses  of  louver  or  blind-work,  with  a  space  of  0".25  between  them,  and  on 
the  north  side  of  one  thickness. 

The  top  of  the  box  was  covered  with  thin  strips  of  deal  2".5  wide,  at  intervals  of  0".75.  Over 
these  crevices  were  placed  strips  of  deal  2".5  wide  raised  0".25  above  the  lower  layer.  A  roof, 
projecting  0"  over  the  south  side,  was  placed  over  the  box,  sloping  to  the  south,  the  southern  edge 
of  the  box  being  1".5  below  the  roof. 

This  construction  permitted  free  circulation  of  air,  but  prevented  the  undue  influence  of  the 
sun,  radiation,  and  currents  of  air. 

The  box  was  securely  attached  to  two  posts  nrmly  driven  into  the  ground  in  the  northern  part 


102  KEPOKT  OF  PROFESSOR  EASTMAN. 

of  the  iuclosure.  Across  the  bottom  of  the  box,  which  was  3'.5  iibovc  tlio  grass,  were  nailed  narrow 
strips  of  deal  to  protect  the  instruments  from  disturbance  from  below. 

The  three  thermometers  were  suspended  from  the  top  of  the  box,  near  the  central  line,  and  the 
barometer  was  placed  on  the  lattices  at  the  bottom.  From  information  received  from  Colonel  J.  W. 
Otley,  engineer  of  the  Des  Moiiies  Valley  railroad,  and  from  the  triangulatiou  of  Professor -Hark- 
ness,  I  find  that  the  barometer  was  833.5  feet  above  the  level  of  the  sea. 

The  solar  thermometer  was  suspended  in  wooden  crutches  4"  above  the  grass  and  0'  south  of 
the  thermometer  box. 

The  actinometer,  when  in  use,  was  attached  to  a  post  near  the  northeast  corner  of  the  inclostire, 
and  the  photometer  was  placed  on  a  stand  directly  south  of  the  actinometer. 

METEOROLOGICAL  OBSERVATIONS. 

Before  the  completion  of  the  observatory  a  daily  record  of  the  weather  was  made,  from  which 
the  following  extracts  are  taken,  showing  the  character  of  the  weather  during-  that  period: 

July  10. — Afternoon  nearly  clear;  wind  northwest.    Evening  hazy,  with  wind  southwest. 

July  11. — Temperature  and  moisture  increasing-.  Many  cirro-cumulus  clouds.  Hazy  in  the 
evening. 

July  12. — Heavy  shower,  with  lightning  and  thunder,  in  the  morning.  Almost  constant  light- 
ning during  the  night,  with  considerable  rain. 

July  13. — Heavy  thunder-shower  in  the  morning,  and  a  very  heavy  one  in  the  evening. 

July  14. — Rain  in  the  morning;  cooler  in  the  afternoon,  and  clear  at  sunset. 

July  15. — From  daylight  until  W'SO111  a.  in.  a  severe  storm  prevailed,  and  from  7h  until  9h  the 
thunder  was  one  continuous  peal.  Slight  showers  at  intervals  during  the  afternoon  and  evening. 
Wind  west  and  northwest. 

July  16. — A  very  severe  storm  came  on  at  7'1  a.  m.,  and  lasted  lour  hours.  For  more  than  two 
hours  there  was  a  continuous  peal  of  thunder.  Clear  at  4h  p.  in. 

July  17. — A  heavy  northeast  storm  during  the  morning.     Clear  at  7h  30'"  p.  in. 

July  18. — A  fair  day;  clear  most  of  the  time. 

July  19. — Thunder-storm  in  the  morning;  clear  at  4h  31)m  p.  m. 

July  20.— A  fair  day.    Wind  north. 

July  21. — A  clear  day.     Wind  north-northwest. 

July  22. — Light  haze  during  the  day. 

July  23. — Hazy  and  quite  warm  during  the  day. 

On  July  22  and  23  the  instruments  were  unpacked  and  mounted,  and  on  July  24  the  obscrva. 
tions  with  the  barometer  and  thermometers  were  commenced  and  continued  every  day  until  August 
9  at  3h  p.  in. 

Having  no  one  but  Mrs.  Eastman  to  assist  me,  I  was  unable  to  make  so  extensive  a.  series  of 
observations  as  I  desired,  for  I  was  obliged  to  devote  a  portion  of  my  time  to  the  use  of  the  actinome- 
ter and  photometer,  and  a  large,  portion  of  Mrs.  Eastman's  time  Was  occupied  in  practice  with  these 
instruments,  and  in  recording  the  observations  which  1  made  with  them.  The  original  plan  was  to 
make  the  observations  every  hour  during  the  day,  but  occasionally  it  was  impossible  to  have  an 
observer  at  hand  when  I  was  necessarily  absent  for  my  meals;  and  there  were  many  breaks  in  the 
series  on  that  account. 

I  am  greatly  indebted  to  Messrs  A.  E.  Le  Merle  and  E.  J.  Ward  for  voluntary  assistance  on 
several  occasions  when  the  observations  would  otherwise  have  been  lost.  On  the  28th  of  July  I 
commenced  the  observations  at  71'  a.  m.,  and  continued  them  hourly  until  7'1  p.  m.  on  the  29th,  but, 
finding  this  too  exhaustive  labor,  I  was  forced  to  abandon  the  observations  during  the  night,  though 
I  was  very  anxious  to  determine  the  march  of  the  temperature  and  atmospheric  pressure  during  the 
entire  day  and  night. 

On  the  morning  of  the  29th  I  commenced  the  observations  with  the  actinometer  and  photome- 
ter at  sunrise,  and  continued  them  as  often  as  practicable  until  sunset.  The  observations  were  fre- 
quently interrupted  by  patches  of  light  haze,  and  I  realized,  more  fully  than  ever  before,  the  fact 
that  perfectly  clear  days  are  extremely  rare  in  August,  even  in  the  unusually  pure  air  of  Iowa. 

Another  series  of  observations  with  the  actiiioineter  was  made  on  August  4,  and,  though  appa- 


OBSERVATIONS   OF   THE    ECLIPSE    OF   AUGUST   7,    1869.  103 

rently  a  clear  day,  the  observations  gave  evidences  of  the  presence  of  light  haze  before  the  snn, 
which,  on  careful  examination,  could  be  detected  by  the  eye. 

The  weather  from  July  24  to  August  5  was  generally  clear  and  pleasant,  with  but  little  rain, 
which  fell  in  showers  of  short  duration.  On  the  5th  of  August  the  wind  had  swung  around  into  the 
fjist,  and  the  sky  was  overcast  with  cumulo-stratus  clouds.  A  few  drops  of  rain  fell  at  8h  a.  m.  and 
again  in  the  afternoon. 

On  the  morning  of  the  Gth  the  wind  was  blowing  hard  from  the  northeast,  and  the  clouds  were 
much  more  dense  than  on  the  5th.  At  II1'  30111  a.  m.  a  misty,  drizzly  rain  commenced,  and  lasted 
until  I1'  .'>0">  ]>.  m.,  when  the  temperature  began  to  rise,  and  there  was  a  change  from  gray  to  black 
in  the  color  of  the  clouds.  The  clouds  grew  darker  and  more  dense  until  dark,  when  it  seemed  that 
a  heavy  northeast  storm  was  unavoidable.  During  the  evening,  telegrams  from  stations  east  and 
west  of  Des  Moines  reported  the  sky  "perfectly  clear"  at  Chicago  and  Davenport,  and  "clear"  at 
Omaha,  while  the  indications  of  a  storm  seemed  to  increase  at  Des  Moines  until  llh  p.  m. 

The  meteorological  observations  for  each  day,  save  August  7.  will  be  found  in  Tables  I  to  VII, 
inclusive.  All  the  corrections,  except  for  elevation,  have  been  applied  to  the  readings  of  the  baro- 
meter ;  and  the  readings  from  the  thermometer  scales  require  no  correction.  The  results  of  the 
observations  with  the  actinometer  on  July  29  and  August  4,  and  with  the  photometer  on  July  29, 
are  given  in  Tables  VIII  and  IX. 

OPERATIONS  ON  SATURDAY,  AUGUST  7. 

At  sunrise  the  whole  sky  was  completely  overcast,  though  the  clouds  were  in  many  places  less 
dense  than  on  the  previous  evening,  and  there  were  some  signs  of  approaching  fair  weather. 

At  this  time  the  wind  was  very  changeable,  and  blew  from  all  points  between  north -northeast 
and  southeast,  increasing  in  force  as  it  swung  around  to  the  southeast,  and  decreasing  as  it  moved 
back  to  the  north-northeast.  At  7h  30m  the  wind  became  steady  from  the  southeast,  and  blew  a  stiff' 
breeze,  while  the  moisture  in  the  atmosphere  became  perceptibly  less  than  on  the  Gth.  At  S1'  the 
clouds  began  to  break  up  into  detached  masses  and  rapidly  disappear.  At  10h  the  force  of  the  wind 
had  abated  considerably,  and  small  masses  of  fleecy  clouds  and  patches  of  light  haze  were  all  that 
remained  of  the  ominous  gloom  of  the  early  morning.  The  observations  with  the  barometer  and 
thermometer  were  commenced  at  91'  a.  m.,  but,  owing  to  the  prevalence  of  drifting  clouds,  the  acti- 
nometer and  photometer  were  not  used  until  II1' a.  m.;  and  even  then  several  attempted  observations 
between  llh  and  noon  were  interrupted  and  spoiled  by  clouds  and  haze. 

About  noon  the  clouds  increased  rapidly  for  a  short  time,  but  soon  began  to  disappear  again, 
and  at  lh  15'"  only  a  light  haze  remained  to  dim  the  brilliancy  of  the  sun.  At  lh  30m  a  few  cumulus 
clouds  were  seen  in  the  west,  but  they  soon  disappeared,  and  the  only  clouds  seen  during  the 
remainder  of  the  afternoon  were  a  few  light  cirri,  which  seemed  to  be  collected  in  the  vicinity  of  the 
sun.  The  haze  remained  during  the  afternoon,  and,  though  at  several  times  it  almost  disappeared 
in  the  immediate  vicinity  of  the  sun,  it  was  generally  a  serious  obstacle  to  the  satisfactory  use  of  the 
actiuomcter  and  photometer.  I  intended  to  make  a  series  of  observations  with  all  the  instruments 
every  half  hour  during  the  afternoon  until  the  time  of  first  contact,  and  then  as  often  as  possible 
until  after  the  last  contact.  The  first  part  of  the  plan  was  accomplished,  but  the  several  readjust, 
ments  of  the  actinometer  column,  which  were  required  by  the  decrease  of  the  direct  solar  heat, 
occupied  more  time  than  I  anticipated,  and  diminished  the  number  of  observations  that  I  had  thought 
it  possible  to  make.  IJesides  using  the  various  meteorological  instruments,  I  decided  to  observe  the 
"first  contact,"  the  beginning  and  end  of  "  totality,"  the  various  phenomena  of  totality,  and  the 
"  last  contact"  of  the  eclipse. 

After  some  conference  with  Professor  llarkness,  I  had  decided  that,  as  the  success  of  the  spec- 
troscopic  observations  depended  greatly  upon  the  rapidity  and  steadiness  with  which  the  instrument 
was  directed  to  the  different  points  to  be  examined,  I  would,  by  means  of  the  finder,  direct  the  tele- 
scope, to  which  he  had  attached  his  spectroscope,  to  the  most  prominent  objects  and,  at  the  same 
time,  note  the  general  phenomena  of  the  totality. 

During  the  afternoon  Mrs.  Eastinan  recorded  my  observations  with  the  actinometer,  the  baro- 
meter, and  the  thermometers,  and  made  the  observations  with  the  photometer,  except  during  totality, 


104  REPORT  OF  PROFESSOR  EASTMAN. 

•when,  \vitli  the  assistance  of  Mr.  D.  P.  Marryatt,  jr.,  of  Chicago  University,  who  kindly  volunteered 
his  services,  she  made  all  the  observations  that  were  obtained  with  the  above  instruments. 

At  two  minutes  before  the  computed  time  of  first  contact  I  took  my  position  at  the  3".5  tele- 
scope, the  aperture  of  which  had  been  reduced  to  l".7o,  and  carefully  examined  the  sun's  disk,  upon 
which  were  seen  very  distinctly  three  groups  of  small  spots  and  two  large  single  spots.  The  c\r- 
piece  used  had  a  power  of  50,  and  I  obtained  a  very  clear  and  well-defined  image. 

The  first  apparent  contact  of  the  limbs  of  the  sun  and  moon  was  observed  on  the  north  \\csi 
limb  of  the  sun  at  9b  59m  22S.5  by  chronometer,  (Negus  1300.)  This  was  several  seconds  later  than 
the  computed  time,  and  from  the  observed  motion  of  the  moon's  limb  for  the  next  five  seconds  I 
concluded  that  the  actual  contact  occurred  from  four  to  five  seconds  before  it  was  detected  by  the. 
eye. 

The  edge  of  the  moon,  as  projected  on  the  sun's  disk,  was  as  sharp  and  well  defined  as  the  limb 
of  the  sun. 

Soon  after  returning  to  the  use  of  the  meteorological  instruments  the  actiuometer  and  photo- 
meter exhibited  a  decided  change  in  the  amount  of  heat  and  light,  but  the  varying  amount  of  ha/.e 
operated  unfavorably  upon  the  attempt  to  ascertain  precisely  when  the  instruments  would  have 
detected  the  change. 

The  decrease  of  heat  and  light  progressed  steadily  until  about  4h  20'",  when  an  unusual  collec- 
tion of  cirri  and  haze  shut  off  a  large  portion  of  the  light  and  heat  of  the  sun,  as  will  be  seen  by 
reference  to  the  observations  or  to  the  curves  on  Plate  VIII,  for  nearly  ten  minutes. 

As  the  eclipse  progressed  the  wind  gradually  decreased  and  blew  in  little  pnffs,  the  sun's  light 
became  visibly  diminished,  the  distant  landscape  assumed  a  different  hue,  and  a  slight  moist  chilli- 
ness seemed  to  pervade  the  air. 

'The  actiuometer  now  needed  careful  attention  and  frequent  adjustment,  and  the  photometer 
showed  that  the  light  was  rapidly  diminishing.  The  landscape  on  the  eastern  bank  of  the  Des 
Moines  River  had  a  greenish-yellow  hue,  as  if  seen  through  tinted  glass,  and  the  shadows  of  the 
trees  had  almost  disappeared.  The  countenances  of  the  observers  had  a  sickly,  ghastly  appearance, 
and  the  peculiar  chilliness  had  increased  until  it  was  ATery  uncomfortable. 

What  sunlight  there  was  left  at  4h  -40m  seemed,  as  it  fell  upon  the  observatory  and  the  adjacent 
grounds,  like  the  feeble  reflected  light  from  a  large  conflagration  at  night.  The  totality  was  now 
near,  and,  after  adjusting  the  actinometer  for  the  observation  during  totality,  I  went  into  the 
observatory  to  prepare  for  the  observations. 

The  object-glass  of  the  finder  which  I  used  for  the  observations  during  the  total  phase  was  0.08 
inch  in  diameter,  and  the  eye-piece  had  a  power  of  10.    The  definition  of  the  sun's  image  as  exam 
ined  before  the  eclipse  was  very  good.    The  neutral-tinted  glass  for  the  protection  of  the  eye  before 
totality  was  in  a  brass  cap  fitting  loosely  over  the  object-glass. 

At  two  minutes  before  the  computed  time  for  the  beginning  of  the  total  phase  I  carefully  exam- 
ined the  portion  of  the  sun  then  visible,  and  also  that  portion  of  the  moon  that  was  well  defined,  and 
found  the  edges  of  both  sharp,  with  no  indentations  or  irregularities  of  any  kind,  and  none  appeared 
until  the  instant  of  totality,  when  the  cusps  of  the  crescent-like  band  of  light  suddenly  became 
obtuse,  and,  retreating  towards  the  central  line  of  the  crescent  with  the  velocity  of  lightning,  the 
last  ray  of  light  disappeared  at  II1'  1™  368.8,  by  Negus  1300. 

The  moment  the  cusps  of  the  sun's  light  became  obtuse  I  removed  the  glass  shade,  so  that  the 
last  view  of  the  light  was  unobstructed  and  not  bright  enough  to  be  disagreeable. 

The  total  obscuration  was  coincident  with  the  appearance  of  the  corona  and  protuberances  and 
with  the  rush  of  a  peculiar,  almost  tangible  darkness.  The  corona  (Figs.  1  and  2,  Plate  IX)  appeared 
as  if  a  screen  had  been  suddenly  withdrawn  to  present  it  as  a  background  for  the  better  exhibition 
of  the  black  body  of  the  moon  and  the  colored  prominences.  I  was  considerably  disappointed  with 
the  appearance  of  the  color  and  brilliancy  as  well  as  with  the  extreme  contour  of  the  corona.  Most 
observers  have  described  the  color  as  "  pure"  or  "clear"  white  and  the  light  as  very  brilliant,  while, 
nearly  all  the  published  sketches  represent  the  contour  as  nearly  circular  and  regular  and  the  coronal 
rays  as  radial  and  equally  distributed  about  the  body  of  the  sun. 

The  color  of  the  corona,  as  I  observed  it  both  with  the  telescope  and  without,  was  a  silvery 
white,  slightly  modified  in  the  outer  portions  by  an  extremely  faint  tinge  of  greenish-violet,  and  ] 


OBSERVATIONS   OF   THE   ECLIPSE   OF   AUGUST   7,    1869. 


105 


could  not  detect  the  least  change  in  the  color  or  in  the  position  of  the  rays  during  totality.  The 
light  of  the  corona  was  not  brilliant — perhaps  from  the  effect  of  haze — but  appeared  more  like  the 
pale  light  from  the  train  of  a  meteor  than  like  anything  else  that  I  could  recall  at  the  time. 

The  corona  seemed  to  be  composed  of  two  portions,  both  visible  to  the  naked  eye,  in  which 
with  the  small  instrument  which  I  used,  I  was  unable  to  trace  any  similarity  of  structure. 

The  portion  nearest  the  sun  was  about  1'  high,  forming  nearly  a  continuous  band  about  the 
sun,  and  appeared  to  be  a  mass  of  nebulous  light,  resembling  in  structure  the  most  brilliant,  irre- 
solvable portions  of  the  milky  way.  Its  color  was  silvery  white  and,  like  its  density,  appeared  the 
same  throughout  its  whole  extent.  The  outer  portion  consisted  of  rays  of  light  arranged  in  two 
different  ways.  In  five  places  they  were  arranged  into  groups  resembling  star  points  composed  of 
slightly  convergent  and  radial  rays,  but  elsewhere  were  disposed  as  radial  lines.  The  color  of  the 
bases  of  the  star  points  and  of  the  radial  lines  was  the  same  as  that  of  the  inner  portion,  while 
the  outer  portion  of  the  points  had  a  very  faint  greenish-violet  tint.  The  radial  lines  were  the 
most  prominent. 

Four  of  the  star  points  project  farther  from  the  sun  than  the  ordinary  radial  lines,  and  give  the 
contour  of  the  corona  the  form  of  a  trapezoid.  Between  the  protuberances  JSTos.  4  and  5  scarcely 
any  corona  was  observed. 

As  the  sunlight  disappeared  the  protuberances  seemed  to  be  thrust  out  from  the  body  of  the 

sun,  and  their  maximum  size  and  their  color  during  totality  is  represented  in  Figs.  1  and  2,  Plate  IX. 

I  immediately  directed  the  spectroscope  to  the  prominence  marked  "3,"  Fig.  3,  and  aftenvards 

o  those  marked  "5"  and 
"  1."  Then  I  directed  it 
to  the  points  in  the  corona 
marked  "CV'and  "C2,"  but 
no  spectra  were  obtained 
until  the  slit  was  directed 
o  that  portion  of  the 
largest  star  point  marked 
"C3."  Thinking  that  the 
end  of  totality  was  near, 
I  took  my  eye  away  from 
the  finder,  and,  seeing  by 
the  chronometer  that 
there  was  yet  consider- 
able time  before  the  reap- 
pearance of  the  sun,  I 
looked  carefully  at  the 
co  ona,  and  at  the  light 
as  it  appeared  to  come 
from  a  peculiar  twilight 
in  the  southwest  for  about 
fifteen  seconds,  when  I 
took  up  the  beat  of  the 
chronometer  in  order  to 
note  the  time  of  the  end 
of  the  total  phase.  Pro- 
fessor Harkness  at  this 
moment  proposed  to  ex- 
amine with  the  spectro- 
scope the  large  prominence  that  was  so  plainly  visible  on  the  sun's  western  limb.  The  instrument 
was  instantly  turned  to  this  prominence,  which  proved  to  be  No.  1,  (previously  examined,)  but  it 
had  increased  nearly  fifty  per  cent,  since  the  first  examination.  In  order  to  vary  the  observation, 
the  instrument  was  directed  to  the  lowest  point  of  the  prominence. 
14* 


106  REPORT  OF  PROFESSOR  EASTMAN. 

Upon  the  completion  of  this  observation  the  instrument  was  directed  to  No.  7,  and  while  in  this 
position  the  limb  of  the  sun  appeared. 

The  protuberance  marked  "1"  was  the  largest  of  the  series,  and  was  the  one  which  most 
attracted  the  attention  of  naked-eye  observers.  The  color  of  this  protuberance,  like  all  the  others, 
was  a  bright  carmine,  a  dark  shade  near  the  base — changing  to  a  bright  pink,  in  Nos.  1,  3,  and  4, 
near  the  top.  A  faint  dark  line,  as  shown  in  Fig.  3,  was  the  only  mark  of  any  kind  observed.  At 
the  time  of  the  second  examination  with  the  spectroscope  this  protuberance  was  very  brilliant  near 
the  base,  but  it  was  at  this  time  that  the  line  was  seen  on  the  southern  portion  and  that  the  upper 
portion  had  a  pinkish  tinge. 

The  color  of  No.  2  appeared  the  same,  from  the  bottom  to  the  top,  and  when  first  seen  there  was 
a  low  line  of  light  stretching  out  toward  the  west,  along  the  edge  of  the  moon.  On  the  eastern 
portion  of  this  protuberance,  and  nearly  parallel  with  its  eastern  boundary,  was  a  dark  line  much 
heavier  than  the  one  in  the  first  protuberance. 

No.  3,  when  first  seen,  was  much  more  curved  than  it  appears  in  Fig.  3.  About  three  seconds 
after  its  first  appearance  it  seemed  to  make  a  half  turn  from  the  left  toward  the  right,  not  gaining 
length  by  the  movement,  when  it  became  fixed  in  the  position  shown  by  the  full  line  in  Fig.  3.  The 
dotted  line  represents  its  outline  before  the  change.  The  color  of  the  upper  portion  of  this  pro- 
tuberance was  very  much  lighter  than  that  of  the  lower — almost  a  light  pink. 

When  No.  4  was  first  seen  it  had  the  flickering  motion  of  an  alcohol  flame  in  a  strong  current 
of  air.  This  motion  was  so  violent  that  at  times  only  a  trace  of  its  light  was  visible  beyond  the 
limb  of  the  moon,  and,  thinking  that  it  would  be  impossible  to  examine  this  prominence  with  the 
spectroscope.  I  concluded  not  to  waste  any  time  in  the  attempt  while  the  motion  continued.  In 
about  thirty  seconds  the  motion  subsided,  and  this  protuberance  became  as  steady  as  No.  1.  At 
that  time  the  upper  portion  had  a  pinkish  tinge.  The  sketch  in  Fig.  1,  Plate  IX,  represents  the 
form  after  the  movement  ceased. 

In  No.  5,  and  the  low  range  of  protuberances  to  the  north  of  it,  the  same  motion  was  observed 
as  in  No.  4,  though  in  No.  5  it  was  not  so  violent,  and  had  ceased  when  the  spectroscopic  examina- 
tion of  No.  3  was  finished.  This  motion  continued  for  some  time  in  the  low  range  of  protuberances 
after  it  ceased  in  No.  5,  but,  owing  to  the  fact  that  my  attention  was  confined  to  the  examination 
of  No.  1,  I  did  not  notice  when  it  ceased — I  only  saw  that  it  was  perfectly  steady  before  the  spec- 
troscopic observations  of  the  corona  were  commenced. 

No.  G,  and  the  low  range  of  protuberances  to  the  north  of  it,  had  the  same  bright  carmine  color 
throughout  their  whole  extent,  but  had  no  motion  that  was  perceptible.  Toward  the  end  of  the 
total  phase  Nos.  6  and  7  became  connected  by  a  lower  ridge  of  the  protuberant  mass,  which  increased 
in  height  until  the  end  of  totality.  No.  7  was  motionless  like  No.  6,  and  was  of  the  same  color. 
While  examining  No.  7  the  sunlight,  preceded  about  ls.5  by  a  lighting  up  of  the  corona,  appeared 
exactly  between  Nos.  0  and  7 — not  as  a  very  attenuated  crescent  of  light,  as  before  the  beginning 
of  totality,  but  like  a  fleecy  flame,  resembling  somewhat,  in  size  and  form,  protuberance  No.  1. 
This  flame  instantly  spread  along  the  edge  of  the  moon,  and  became  immediately  too  strong  for  the 
eye.  The  appearance  of  this  light  occurred  at  llh  4m  348.0  by  Negus  1300.  I  immediately  made  the 
sketches  of  the  corona  (Fig.  3)  and  the  protuberances,  (Figs.  1  and  2,  Plate  IX,)  and  wrote  out  my 
notes  on  the  appearance  of  the  various  phenomena.  Figs.  3  and  4,  and  Figs.  1  and  2,  Plate  1 X , 
were  sketched  from  the  appearance  of  the  objects  in  the  reversing  telescope. 

While  my  eye  was  away  from  the  finder,  just  after  the  examination  of  the  corona,  I  gave  a  few 
seconds  time  to  the  observation  of  the  peculiar  light.  Owing  to  my  position  in  the  observatory,  1 
could  see  only  the  western  sky,  in  which  the  darkest  portion  was  just  outside  the  bounding  lines  of  the 
corona.  This  portion  of  the  sky  had  a  dark  slate  color,  changing  toward  the  southwest  to  a  leaden 
hue,  but  maintaining  its  dark  slate  color,  with  but  little  modification,  as  far  east  and  north  as  I  could 
see.  This  dark  color  prevailed  in  the  sky  west  of  the  sun  nearly  down  to  the  horizon.  Near  the 
horizon  in  the  southwest  the  light  resembled  that  of  a  hazy  twilight,  slretchiug  as  far  south  as  I 
could  see  and  to  a  point  in  the  western  horizon  west  15°  south.  To  the  northward  of  this  point 
there  was  a  narrow  band  of  grayish  light  on  the  horizon.  From  my  point  of  observation  it  seemed 
that  all  the  light  we  received  (a  very  small  amount)  came  from  this  southwestern  twilight,  though 
Mrs.  Eastman  observed  a  similar  phenomenon  in  the  northeast. 


OBSERVATIONS   OP   THE   ECLIPSE    OF   AUGUST    7.    1869. 


107 


I  coukl  detect  110  resemblance  between  the  light  during  totality  and  that  of  the  rnoou,  and  can 
conceive  of  no  way  in  which  a  comparison  could  be  instituted,  except  by  comparing  the  light  in 
shadows  of  equal  magnitude  in  both  solar  and  lunar  eclipses.  The  light  more  nearly  resembled 
that  from  a  faint  twilight,  about  the  time  of  the  appearance  of  second-magnitude  stars.  On  re- 
turning to  the  meteorological  observations,  I  noticed  that  the  shadows  were  becoming  deeper,  and 
the  chilliness,  so  marked  during  totality,  had  nearly  passed  away. 

I  found  that  Mrs.  Eastman  had  made  the  desired  observations  with  the  actinoineter  and  solar 
thermometer,  but  on  attempting  the  observations  with  the  photometer  she  found  the  light  was 
insufficient  to  render  the  least  trace  of  the  "  star"  at  the  base  of  the  photometer  visible.  On  being- 
assured  by  Mr.  Marryatt  that  the  aperture  was  fully  open,  another  observation  was  attempted,  but 
the  "star"  was  not  visible.  A  third  attempt  resulted  in  a  similar  failure. 

She  then  gave  up  the  observation  as  hopeless,  and,  for  the  first  time,  looked  at  the  corona  and 
protuberances  for  a  few  seconds,  when,  thinking  that  her  eye  had  become  accustomed  to  the  pecu- 
liar darkness,  she  made  another  attempt,  with  the  same  result  as  before. 

On  the  reappearance  of  the  limb  of  the  sun  the  "  star"  could  at  first  be  seen  only  as  a  faint, 
blurred  image,  but  gradually  the  points  of  the  "star,"  then  the  ring,  and  finally  the  dot,  appeared 
by  the  light  from  the  full  aperture. 

The  observations  with  the  photometer,  barometer,  and  thermometers  were  resumed  at  4h  55m, 
and  continued  without  interruption  until  6h. 

The  work  with  the  actinometer  was  recommended  at  5h  15m,  and  continued,  with  a  short  inter- 
val at  the  time  of  the  last  contact  of  the  limbs  of  the  sun  and  moon,  until  6h. 

Tta4 


A  few  minutes  before  the  last  contact  I  carefully  examined  the  disk  of  the  sun  with  the  3.5-iuch 
telescope,  and  made  the  sketch  of  the  solar  spots  a.s  seen  in  Fig.  4. 

The  last  contact  was  observed  with  the  3.5-inch  telescope,  with  the  aperture  reduced  to  1.75 
inch,  and  occurred  at  12h  lm  32S.5  by  Negus  1300.  After  G1'  the  western  sky  became  so  obscured  by 
cirrus  clouds  and  haze  that  no  more  meteorological  observations  were  attempted. 

The  observations  on  the  7th  will  be  found  in  Tables  X,  XI,  XII,  and  XIII,  and  the  results  are 
graphically  represented  in  Plates  VI,  VII,  and  VIII. 


108  REPORT  OF  PROFESSOR  EASTMAN. 

The  curves  for  the  barometer  and  dry  and  wet-bulb  thermometers  show  but  little  deviation  from 
the  curve  deduced  from  twelve  days'  observations.  The  solar  thermometer  shows  the  greatest 
change,  and,  as  will  be  seen  by  reference  to  Table  XIII,  was  lower  eight  minutes  after  totality  than 
during  that  phase. 

The  curves  deduced  from  the  observations  with  the  actinometer  and  photometer  fail,  on  account 
of  the  variable  effect  of  the  haze,  to  give  that  nice  determination  of  the  rate  of  the  change  in  heat 
and  light  which  I  am  confident  they  would  have  done  under  a  clear  sky.  The  same  is  true  of  the 
results  of  the  observations  Avith  the  solar  thermometer.' 

Actinometer: — This  instrument  worked  better  than  I  expected  it  would,  though  it  is  larger  in 
many  respects  than  is  necessary.  The  scale  is  very  easily  read,  and  I  found  that  under  ordinary 
circumstances  no  assistant  was  needed  in  making  and  recording  the  observations. 

Photometer. — lielying  on  the  accuracy  of  the  statement  of  former  observers,  that  the  light  during 
a  total  eclipse  was  equal  to  that  of  the  full  moon,  the  photometer  was  so  constructed  as  to  show  the 
"star"  with  less  light  than  that  of  the  full  moon  at  an  altitude  of  30°.  I  was  convinced,  after  my 
observations  at  Des  Moines,  that  moonlight  was  not  a  proper  standard  of  comparison,  and  after 
my  return  to  Washington  I  made  a  series  of  observations  with  the  photometer  on  the  decrease  of 
light  after  the  disappearance  of  the  sun  and  when  there  were  no  clouds. 

I  found  that  the  appearance  of  the  light  after  sunset  was  very  nearly  like  that  during  the  eclipse, 
and  the  results  of  the  several  comparisons  are  given  below  in  the  same  terms  as  in  Table  IX.  From 
several  series  of  observations  made  in  Des  Homes  I  found  the  observations  of  Mrs.  Eastman  and 
myself  so  nearly  identical  that  the  differences  were  not  appreciable  in  the  terms  given  in  Table  IX, 
so  that  the  following  observations  of  the  disappearance  of  the  "ring"  will  be  comparable  with 
those  made  during  the  eclipse. 

The  following  observations  were  made  with  the  "ring"  until  it  entirely  disappeared  at  C,,  15™, 
and  afterwards  with  the  "star"  until  it  was  too  dark  to  read  the  divisions  on  the  pinion-head.  The 
sun  disappeared  at  5h  57m. 

Time.  Area.  Tirue.  Avon, 

/i.       7H.       *.  sq.  in.  li.      m.       s.  sq.  in. 

COO                0. 01                                0     17  30  0.21 

650                0.64                                      20  0  0.55 

6     10       0                0.74                                .     22  30  0.59 

12    30                1.39                                     25  0  0.66 

15      0               1. 93                                    27  ,30  0. 74 

30  0  0. 96 

32  30  1. 00 

35  0  1. 21 

At  6h  32m  saw  Saturn  and  Antares,  and  at  6,,  35m  saw  second-magnitude  stars. 

At  6h  40m  a  faint  trace  of  the  "  star"  could  be  seen ;  still  a  trace  at  6h  45m,  at  which  time  all 
the  stars  in  the  "Dipper"  could  be  seen.  No  trace  of  the  "star"  at  6h  47m  30s. 

From  the  above  observations  and  from  my  impressions  at  the  time  of  the  total  phase  of  the 
eclipse,  I  conclude  that  the  light  during  the  totality  on  August  7  was  about  equal  to  that  on  a  clear 
moonless  evening,  at  the  time  when  third-magnitude  stars  can  be  easily  seen. 

Chronometers. — The  chronometers  were  taken  out  of  the  gimbals  in  Washington  and  packed  in 
cotton  in  a  small  box  divided  into  three  compartments.  This  box  was  carried  in  the  hand,  except 
when  in  the  cars,  and  was  in  the  care  of  Dr.  Curtis  from  Washington  to  Des  Moines.  From  the 
time  they  left  Washington  until  they  were  packed  to  return  I  wound  them  every  day,  and,  taking 
No.  1300  as  the  standard,  compared  them,  with  one  exception,  every  day.  After  the  observatory 
was  completed  they  were  replaced  in  their  boxes,  and  No.  1300  placed  in  the  photographic  "  dark 
room."  Professor  Harkness  used  1319,  and  Dr.  Curtis  timed  his  photographic  experiments  and 
work  by  No.  1275.  On  returning  to  Washington  they  were  repacked  in  cotton,  as  before,  and  car- 
ried by  Mr.  A.  E.  Le  Merle.  On  July  3,  before  leaving  Washington,  No.  1275  was  5h  10m  43S.5,  No. 
1300  was  5h  9m  41'.5,  and  No.  1319  was  5h  llm31s.O  fast  of  Washington  mean  time.  On  the  31st  of 
August,  after  returning  from  Des  Moines,  No.  1275  was  5h  llm  18.9,  No.  1300  was  5h  9m  358.6,  and 
No.  1319  was  5b  12™  3S.9  fast  of  Washington  mean  time. 


OBSERVATIONS    OF    THE    ECLIPSE    OF   AUGUST   7,    1809.  109 

Time. — According  to  the  determinations  of  Professor  Harkness,  the  error  of  No.  1319  at  the 
time  of  the  eclipse  was  Ch  18m  178.2  fast  of  local  mean  time.  No.  1300  was  compared  with  No.  1319 
three  times  on  the  7th  August,  with  the  following  results: 

It.    m.    .s-.  It.    m.    .v.  //.    m.    *. 

No.  1300 300  12     30    0  1C     8      0 

No.  1319: 3       8       8.0  12     32     8.0  1010      8.7 

Taking,  from  the  above  comparisons,  the  error  of  No.  1303  to  be  2lu  88.0  less  than  that  of  No. 
1319,  we  have  No.  1300  G'1 1C™  8».C  fast  of  local  mean  time. 

Applying  this  error  to  the  times  of  contact,  &c.,  which  I  observed,  we  have 


First  contact 3     43     13.9  j 

1.2  f. 


It.       m.         H. 

3     43     13, 

Beginning  of  totality 4    45    28— v  , 

_    .     „,  n*  A  >  -Local  mean  time. 

End  ot  totality 4    48    25.4  C 

Last  contact 5    45    23.9 ) 

Duration  of  total  phase 2    57.2 

The  meteorological  observations  were  timed  b}1  a  pocket- watch  showing  exact  local  mean  time. 
The  night  of  the  10th  of  August  was  so  cloudy  that  no  meteors  were  seen.    A  A^ery  few  were 
seen  on  the  evening  of  the  9th,  but  there  were  no  indications  of  an  unusual  display. 

After  the  eclipse  most  of  my  time  was  devoted  to  the  preparation  of  a  copy  of  my  observations 
and  notes,  which  I  forwarded  by  express  to  the  Observatory  in  Washington. 

"When  this  work  was  completed  and  the  instruments  packed,  I  left  Des  Moines  as  soon  as  pos- 
sible, and  reached  Washington  on  the  29th  of  August. 

To  the  citizens  of  Des  Moines  I  am  greatly  indebted  for  the  many  social  courtesies  which 
rendered  the  trip  to  that  city  one  to  be  remembered  with  the  greatest  pleasure. 

The  thanks  of  the  party  are  due  the  officers  of  the  Northern  Central,  the  Pennsylvania  Central, 
and  the  Chicago,  liock  Island  and  Pacific  Hallways  for  favors  received  while  passing  over  their 
respective  roads. 

Very  respectfully,  your  obedient  servant, 

JOHN  E.  EASTMAN, 
Professor  of  Mathematics  United  States  Navy. 
Commodore  B.  F.  SANDS,  U.  S.  N., 

Superintendent  United  States  Naval  Observatory,  Washington,  D.  C. 


110 


REPORT    OF   PROFESSOR    EASTMAN. 


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112 


REPORT    OF   PROFESSOR   EASTMAN. 
TABLE  V.— WEATHER. 


Day. 

Hour. 

Clouds. 

Portion 
cloudy. 

Wind. 

Day. 

Hour. 

Clouds. 

Portion 
cloudy. 

Wind. 

3irectiou. 

•''orce. 

direction. 

Torce. 

1869. 

1869. 

July    24 

9 

Clear 

0 

SW. 

3 

July    28 

7 

Clear 

0 

XW. 

1 

10 

Clear 

0 

sw. 

3 

8 

Clear 

0 

N\V. 

1 

11 

Clear 

0 

SW. 

3 

9 

Clear 

0 

W. 

1 

Noon 

Clear 

0 

sw. 

4 

10 

Clear 

0 

N. 

2 

1 

Clear 

0 

sw. 

4 

11 

Clear 

0 

N. 

2 

2 

Clear 

0 

sw. 

4 

Noon 

Clear 

0 

N. 

2 

3 

Clear 

0 

sw. 

5 

1 

Clear 

0 

N. 

2 

4 

Clear 

0 

sw. 

4 

2 

Clear 

0 

N. 

2 

5 

Clear 

0 

sw. 

3 

3 

Clear   - 

0 

N. 

2 

6 

Clear 

0 

sw. 

2 

4 

Clear 

0 

N. 

2 

9 

Clear 

.0  ' 

sw. 

1 

5 

C'leai- 

0 

N. 

2 

.6 

Clear 

0 

N. 

1 

July    25 

9 

C.  K.  S. 

10 

NW. 

1 

7 

Clear 

0 

XW. 

1 

10 

C.  K.  S. 

10 

NW. 

1 

8 

Clear 

0 

XW. 

1 

11 

C.  K.  S. 

10 

NW. 

2 

9 

Clear 

0 

x\v. 

1 

Noon 

C.S. 

10 

NW. 

2 

10 

Clear 

0 

NW. 

1 

1 

C.K. 

10 

NW. 

1 

11 

Clear 

0 

XW. 

1 

2 

C.K. 

10 

NW. 

2 

3 

C.K. 

10 

NW. 

1 

July    29 

0 

Clew- 

0 

NW. 

1 

4 

C.K. 

10 

NW. 

1 

1 

Clear 

0 

NW. 

1 

5 

C.  K.&N. 

10 

NW. 

1 

2 

Clear 

0 

NW. 

1 

• 

* 

3 

Clear 

0 

NW. 

1 

July    26 

8 

C.K. 

1 

NW. 

2 

4 

S. 

Slight 

XW. 

1 

9 

Clear 

0 

xw. 

3 

5 

S.' 

1 

NW. 

1 

10 

Clear 

0 

NW. 

3 

6 

C. 

Slight 

NW. 

1 

11 

Clear 

0 

xw. 

2 

7 

C. 

Slight 

N. 

1 

Noon 

Clear 

0 

NW. 

2 

8 

C. 

Slight 

NE. 

1 

1 

Clear 

0 

NW. 

1 

9 

C.K. 

2 

N. 

1 

2 

Clear 

0 

NW. 

1 

10 

Clear 

0 

N. 

1 

3 

Clear 

0 

NW. 

1 

11 

Clear 

0 

N. 

1 

4 

Clear 

0 

NW. 

1 

Noon 

Clear 

0 

X. 

1 

5 

Clear 

0 

NW. 

1 

1 

Clear 

0 

NW. 

1 

6 

Clear 

0 

NW. 

1 

2          Clear 

0 

N. 

1 

7 

Clear 

0 

NW. 

1 

3 

Haze" 

1 

N. 

1 

8  . 

Clear 

0 

NW. 

1 

4 

Haze" 

1 

N. 

1 

9 

Clear 

0 

NW: 

1 

5 

Clear 

0 

NW. 

1 

(i 

Haze* 

1 

N. 

1 

July    27 

7 

Clear 

0 

NW. 

1 

7 

C.S. 

4 

NW. 

1 

9 

Clear 

0 

NW. 

1 

10 

Clear 

0 

NW. 

1 

July    30 

7 

Clear 

II 

SW. 

1 

11 

Th'kha/e 

10 

S.  SW. 

1 

9 

Clear 

0 

sw. 

1 

Noon 

Haze  C.K 

10 

S. 

1 

11 

Clear 

0 

sw. 

1 

1 

C.K. 

10 

S. 

1 

Noon 

Clear 

0 

sw. 

1 

2 

C.K. 

10 

S. 

1 

1 

Clear 

0 

sw. 

1 

3 

N. 

10 

sw. 

1 

3 

Clear 

.      0 

sw. 

1 

4 

N. 

10 

NE. 

1 

5 

Clear 

0 

sw. 

1 

5 

N. 

10 

NE. 

1 

*  In  tli< 

west. 

OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST    7,    1809. 
TABLE  V.— WEATHER— Continued. 


113 


Wind. 

Wind. 

Day, 

Hour. 

Clouds. 

Portion 
cloudy. 

Day. 

Hour. 

Clouds. 

Portion 
cloudy. 

Direction. 

Force. 

Direction. 

Force. 

1869. 

July    31 

f, 

Clew 

0 

SW. 

1 

Aug.      5 

8 

N. 

10 

E. 

2 

9 

Clear 

0 

8W. 

1 

9 

C.  K.  S. 

10           E. 

2 

Noon 

Clear 

0 

SW. 

1 

10 

C.  K.  S. 

10 

E. 

2 

:s 

Cleat 

0 

SW. 

1 

11 

K.S. 

9 

E. 

2 

fl 

C.  S. 

3 

SW. 

1 

Noon 

K.S. 

8 

E. 

3 

1         K.  S. 

8 

E. 

3 

Aug.      1 

9 

C.  Haze 

10 

SE. 

1 

2 

K.S. 

10 

E. 

2 

3 

C.  Haze 

8 

SW. 

1 

3 

K.S. 

9 

E. 

2 

4 

K.S. 

9 

E. 

3 

Aug.     y 

9 

C.  K. 

9 

NW. 

1 

5 

K.S. 

9           E. 

3 

10 

C.K. 

8 

N. 

1 

6 

K.S. 

10           E. 

2 

It 

C.K. 

f> 

N. 

2 

Noou 

C.  K. 

4 

N. 

1 

1 

C.K. 

S 

N. 

1 

Aug.      fi 

9 

K.S. 

10 

NE. 

3 

9 

C.K. 

3 

N. 

1 

10 

K.S. 

10 

NE. 

3 

:i 

C.K. 

3 

N. 

1 

11 

K.S. 

10           NE. 

3 

4 

C.K. 

2 

X. 

1 

Noon 

N. 

10           NE. 

3 

5 

C.K. 

2 

N. 

1 

1 

N.                      10           NE. 

3 

i; 

C.K. 

1 

N. 

1 

2 

N. 

10           NE. 

2 

3         K.  8. 

10           NE. 

3 

Aug.      3 

7 

Clear 

0 

SE. 

I 

4         K.  8. 

10 

N.  NE. 

3 

8 

Clear 

0 

SE. 

1 

5 

•K.  8. 

10 

N.  NE. 

3 

9 

Clear 

0 

SE. 

1     ii 

(i 

K.S. 

10    •       N.NE. 

3 

10 

Clear 

0 

SE. 

1 

11 
Noon 

Clear 
Clear 

0 
0 

SE. 
SE. 

1 

1 

Aug.      rf 

9 
10 

C.K. 
C.K. 

1           SE. 

1         '  SE. 

2 
2 

1 

K. 

1 

SE. 

1 

11 

Clear 

0           SE. 

1 

2    . 

K. 

1 

SE. 

1 

Noou 

Clear 

0 

SE. 

2 

3 

K. 

1 

S. 

1 

1 

Clear 

0 

SE. 

2 

4 

K. 

Slight 

S. 

I 

2 

Clear 

0 

SE. 

3 

5 

C.K. 

1 

S. 

1 

3 

Clear 

0 

SE. 

2 

6 

C.K. 

1 

S. 

1 

4 

Clear 

0 

SE. 

2 

7 

K.S. 

2 

Calm 

0 

5 

Clear 

0 

SE. 

2 

8 

C.  K.  S. 

4 

NW. 

1 

6 

Clear 

0 

SE. 

1 

Aug.     4 

8 

Clear 

0 

S. 

2 

9 

Clear 

0 

S. 

2 

Aug.     9 

9 

C. 

2 

SE. 

2 

10 

Clear 

0 

S. 

2 

Noou 

C.K. 

5 

SE. 

2 

11 

Clear 

0 

S. 

3 

O 

C.K. 

3 

SE. 

2 

Noon 

Haze 

Slight 

S. 

2 

1 

Haze 

Slight 

S. 

2 

2 

Haze 

Very  slig't 

SW. 

1 

3 

Haze 

Very  slig't 

SW. 

2 

4 

Haze 

Slight 

SW. 

2 

5 

C.  Haze' 

1 

SW. 

1 

6 

C.  Haze* 

1 

SW. 

1 

*  In  the 

west. 

| 

15* 


114 


REPORT  OF  PROFESSOR  EASTMAN. 


TABLE  VI.— EXTREME  TEMPERATURES. 


Day.      . 

Maximum. 

Minimum. 

Day. 

Maximum. 

Minimum. 

o 

o 

o 

o 

July        24 

90.5 

67.0 

August     1 

87.5 

73.5 

25 

75.5 

57.0 

2 

87.5 

64.0 

26 

83.5 

62.0 

3 

91.0 

70.  5 

27 

85.8 

60.3 

4 

94.0 

70.0 

28 

76.0 

52.0 

5 

73.3 

60.0 

29 

79.0 

53.0 

6 

65.0 

59.0. 

30 

82.0 

59.0 

8 

80.5 

56.5 

31 

85.5 

63.5 

9 

88.0 

65.0 

RAIN. 

[No  measurements  were  made  before  July  24.] 


July       25.     Rain  at  lh  a.  m.    Amount 

27.    Rain  during  the  afternoon.     Amount 


0.42    inch. 
0.135  inch. 


August     2.    Light  rain  at  lh  a.  m.     Amount       .....  -        0.085  inch. 

5.  A  few  drops  of  rain  at  8h  a.  m.  and  4h  p.  m. 

6.  A  light,  drizzling  rain  from  11"  30m  a.  m.  to  I1'  30™  p.  m. 


Total  amount  .  •      .  •      -         - 0.640  inch. 

The  following  table  exhibits  the  meaii  results  of  the  meteorological  observations  on  July  24, 
25,  26,  27,  28,  29,  and  August  2,  3,  4,  5,  6,  and  8.  On  July  25  and  27  no  observations  were  made 
at  Ch.  This  fact  will  explain  the  anomalous  results  at  that  hour. 


TABLE  VII. 


¥T/mv 

Thermometers. 

-tiour. 

Barometer. 

Dry. 

Wet. 

Solar 

in. 

o 

o 

0 

9 

29.09 

73.3 

67.6 

112.7 

10 

29.08 

74.3 

68.1 

115.6 

11                  29.  07 

76.1 

68.5 

118.6 

Noon 

29.06 

76.6 

68.9 

119.6 

1 

29.05 

78.2 

69.5 

121.6 

2                  29.04 

78.4 

69.4 

117.4 

3 

29.03 

78.3 

69.3 

115.0 

4 

29.  035 

77.1 

69.0 

106.1 

5 

29.04 

76.0 

68.8 

95.0 

6 

29.05 

76.2 

69.5 

87.5 

The  curves  in  Plates  VI  and  VII  were  constructed  from  the  data  in  the  above  table  and  from 
the  observations  on  the  7th. 


OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST    7,    1869. 


115 


The  following  table  shows  the  mean  results  of  the  observations  with  the  actinoineter  on  July 
29  and  August  4.  The  solar  eftect  is  given  in  millimetres,  and  21mm.7  represents  1°  Fahrenheit- 
The  exposures  were  30  seconds  in  each  case. 

TABLE  VIII. 


Date  and  observation. 

Remarks. 

Date  and  observation. 

Remarks. 

It.     m.        mm. 

A.    in.         mm. 

July  29    6    40        12.6 

Aug.   4    8    30        13.9 

78         16.  0 

90        12.  8 

Haze. 

7     35         14.  7 

9    30       -14.8 

8     10         16.3 

10      0        16.  7 

8     47         16.6 

10    30        17.0 

90         17.  3 

11      0        16.7 

9    35        16.8 

11     30        15.  1 

Lower  cap  oft'  shading  tube. 

10     10        17.2 

12      0        13.6 

Hazy. 

10    32        17.  8 

1      0        14.0 

Hazy. 

11      8        20.8 

1     30        14.2 

Hazy. 

12      5        23.  8 

20        13.  9 

Hazy. 

1     15        25.  4 

2    30        14.7 

Hazy. 

2    20        22.1 

30         11.8  :  Hazy. 

32        14.2 

Hazy. 

3    30        12.4  :  Hazy. 

4    42        15.  0 

Hazy. 

40        11.6 

Hazy. 

50        10.  8 

Hazy. 

4    30          8.7 

Very  hazy.                   [and  haze. 

5    25         10.4 

5      0         12.  4 

Sun  shining  through  rift  in  cirri 

60          7.9 

Hazy. 

5    30          3.5     Cloudy. 

At  6h  30™  two  minutes  exposure  produced  no  effect  on 

At  tih  SO"1  the  sun  was  olisrurcd  by  cirrus  clouds. 

the  height  of  the  column. 

OBSERVATIONS  WITH  THE  PHOTOMETER. 

The  following  table  shows  the  variations  in  the  area  of  the  aperture  through  which  light  is 
admitted  to  the  photometer  tube  to  render  the  "ring"  in  the  "star"  visible.  The  area  is  given 
in  square  inches. 

TABLE  IX. 


7(. 

m. 

Area. 

ft. 

m. 

Area. 

July  2U        4 

30 

1.10 

July  29        I 

0 

0.02 

4 

45 

0.26 

2 

0 

.02 

5 

0 

.06 

3 

0 

.06 

5 

15 

.04 

3 

30 

.07 

5 

30 

.04 

4 

30 

.07 

5 

45 

.04 

5 

0 

.10 

6 

0 

.04 

5 

30 

.08 

7 

0 

.06 

5 

45 

.10 

8 

0 

.03 

6 

(1 

.09 

9 

0 

.03 

6 

30 

.11 

10 

0 

.01 

7 

0 

.12 

11 

0 

.01 

7 

ir> 

.12 

12 

0 

.004 

116 


REPORT    OF   PROFESSOR    EASTMAN. 


TABLE  X.— ACTINOMETER  OBSERVATIONS,  AUGUST  7,  1869. 


£ 

•d  -a 

'      -  j^ 

; 

§ 

Sun 

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O 

o 

1 

Hour. 

S* 

V 
CM 

O 
rtt 

O 
Shade 

First 
reading. 

Second 
reading. 

Change  — 

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v 

*S  '* 

2 
s  3 

ll 

1 

3 

is 

'i£  ^   ^ 

E-  " 

*^2 

s 

§3          © 

In  snn. 

In  shade. 

• 

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£ 

£ 

~. 

^ 

EC 

n 

H 

& 

B 

h.   m.  8. 

8. 

mm. 

mm. 

ram. 

Will. 

mm. 

HI  HI. 

0 

mm. 

HI  HI  . 

0 

14.0 

19.2 

5.2 

© 

17.0 

9.  5 

—    7.5 

11.9 

11.7 

O 

10.8 

11.3 

3.5 

© 

13.0 

8.0 

-    5.0 

10.6 

10.4 

o 

21.2 

29.0 

7.8 

11     0     0 

30 

© 

;io.  o 

26.3 

-    3.7 

10.7 

224.5 

67.0 

10.5 

10.8 

0 

27.2 

33.5 

6.3 

© 

35.0 

28.0 

-    7.0 

11.2 

11.0 

0 

25.5 

27.5 

2.0 

© 

32.5 

16.0 

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10.  5 

10.3 

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19.5 

6.0 

©         la  r» 

13.5 

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O             87.8 

95.  8 

8.0 

12     0     0       30          0             95.0 

92.0 

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224.5 

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88.0 

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©            86.  5 

82.5 

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O             58.  0 

67.5 

9.  5 

©             72.  8 

69.0 

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14.1 

13.8 

0 

72.8 

83.8 

11.0 

i  :;o   o 

30 

© 

85.5 

82.0 

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14.5 

224.  5 

69.0 

14.2 

14.  Of 

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97.0 

11.0 

© 

98.8 

94.8 

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14.3 

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97.0 

106.5 

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130.  5 

137.0 

0.5 

© 

139.8 

135.0 

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11.3 

11.1 

o 

135.0 

141.5 

6.5 

200 

30 

© 

140.  5 

136.5 

4.0 

10.4 

224.  5 

72.0 

10.2 

10.7$ 

0 

138.5 

144.8 

6.3 

© 

143.8 

139.0 

-    4.8 

10.9 

10.7 

0 

139.3 

142.5 

5.9 

0 

153.5 

161.0 

7.5 

© 

160.0 

155.0 

—    5.  0 

12.2 

12.0 

2  30     0 

30 

o 

156.5 

163.5 

7.0 

224.5 

73.0 

10.  9f 

© 

164.0 

161.0 

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10.0 

9.8 

o 

164.5 

171.5 

7.0 

o 

101.0 

110.0 

9.0 

© 

115.5 

U3.5 

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11.1 

10.9 

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118.3 

127.5 

9.2 

300 

30 

© 

128.  .0 

125.8 

—    2.2 

10.6 

224.5 

72.0 

10.4 

10.4 

o 

130.0 

137.5 

.  7.5 

© 

140.2 

138.0 

—    2.2 

10.2 

10.0 

0 

142.5 

151.0 

8.5 

i 

*  Interrupted  by  clouds. 


t  Cloudy. 


J  Clear. 


§  Hazy. 


OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST    7,    1869. 


117 


TABLE  X.— ACTINOMETEB  OBSERVATIONS,  AUGUST  7,  1869— Continued. 


g 

"3  -d 

*S 

_^ 

Hour. 

iodof  expoKii 

Sun 

0 

Shade 

First 
rciiding. 

Second 
reading. 

• 
Change  — 

ar  eft'ect. 

?! 

i%° 

literature  < 
liquid. 

aj    ^3 

Jt-H          QJ 

'—        7" 

®   a 

•e 

in  solar  effec 

1 

® 

In  sun. 

In  shade. 

i 

i-3* 

£ 

1 

u 

s 

h.  m.  «. 

». 

mm. 

•mm. 

mm. 

mm. 

mm. 

mm. 

o 

mm. 

mm. 

O 

139.  5 

147.5 

8.0 

® 

148.  5 

147.0 

1.5 

10.5 

10.3 

3  30     0 

30 

O 

152.0 

162.  0 

10.0 

222.  H 

68.0 

10.8 

® 

163.0 

161.0 

-    2.0 

11.5 

11.2 

0 

167.0 

176.0 

9.0 

o 

101.8 

108.0 

6.2 

© 

110.5 

109.0 

•     1.5 

7.9 

7.7 

400 

30 

0 

108.0 

114.5 

6.5 

222.8 

66.0 

7.6 

© 

115.0 

112.5 

—    2.5 

7.7 

7.5 

O 

113.0 

117.0 

4.0 

0 

151.0 

154.5 

3.5 

© 

154.0 

151.0 

-     3.0 

6.2 

6.1 

4  10    0 

30 

o 

151.5 

154.  "> 

3.0 

222.5 

67.0 

5.2 

© 

153.0 

151.0 

-    2.0 

4.3 

4.2 

o 

149.4 

151.0 

1.6 

0 

149.0 

149.  5 

,5 

© 

149.0 

144.  5 

—     4.5         4.9 

* 

4.8 

4  20     0 

30 

0 

143.0 

143.  3 

.3 

222.  5 

67.0 

4.  3 

© 

141.5 

137.  5 

4.0 

3.  9 

_  :i.  8 

0 

136.8 

136.  0 

—      .5 

0 

125.  5 

123.5 

—    2.0 

© 

120.0 

115.0 

-    5.0 

2.8 

2.7 

4  30    0 

30 

o 

112.5 

110.0 

—    2.5 

222.  5 

65.0 

2.5 

© 

106.5 

101.5 

-    5.0 

2.5 

2.4 

0 

98.0 

95.5 

—    2.5 

o 

76.5 

73.5 

—    3.0 

© 

69.  5 

64.5 

—    5.0 

1.8 

1.8 

4  35    0 

30 

0 

59.5 

56.0 

—    3.5 

222.  5 

83.0 

1.3 

© 

53.  0 

48.5 

4.5 

.8 

.8 

0 

46.  5 

42.5 

-    4.0 

4  45     0 

30 

o 

17.2 

16.4 

—      .8 

1  45  30 

© 

16.4 

15.6 

-      .8 

.0 

222.  5 

61.0 

0.0 

o 

157.0 

156.0 

•     1.0 

© 

152.2 

148.0 

-     4.2 

3.4 

3.3 

5  15     0 

30 

0 

145.  5 

144.9 

.6 

221.5 

66.0 

3.2 

ffi 

.143.  0 

139.3 

—     3.7 

3.1 

3.0 

0 

137.5 

137.0 

—       .5 

118 


REPORT    OF    PROFESSOR   EASTMAN. 


TABLE  X.— ACTINOMETER  OBSERVATIONS,  AUGUST  7,  1869— Continued. 


9 
C 

•c  -a 

fad 

i 

_^ 

• 

Sun 

'5   a 

= 

v 

,t 

Hour. 

Period  of  expo 

0 

Shade 
0 

First 
reading. 

Second 
reading. 

Change  — 

Solar  eft'ect. 

»s  J 

"*-   £ 

o 

Q 

Pi 

Temperature 
liquid. 

Sfc      V 
0     g 

.    -5 

rt 

1 

Mean  solar  eft 

In  sun.      In  shade. 

A.  m.  s. 

s. 

mm. 

mm. 

mm.             mm. 

mm. 

mm. 

o 

mm. 

mm. 

0 

122.5 

120.8 

1-7 

© 

117.0 

111.0 

-    6.0    . 

4.3 

4.2 

5  30    0 

30 

O 

116.5 

114.8 

1.7 

221.5 

65.0 

4.0 

© 

100.5 

95.0 

—    5.5 

3.9 

3.7 

O 

91.0 

89.5 

1.5 

O 

51.5 

50.3 

1.2 

© 

48.0 

43.0 

—    5.0 

3.9 

3.8 

5  50    0 

30 

O 

39.0 

38.0 

" 

221.5 

62.0 

4.3 

© 

33.8 

28.0 

i  —    5.8 

4.9 

4.8 

o 

25.3 

24.5 

—     -.8 

o 

3.4 

3.3 

.1 

© 

3.0 

2.6 

.4 

.2 

.2 

600 

30 

0 

2.4 

2.2 

.2 

221.  5 

55.0 

0.2 

© 

2.0 

1.6 

.4 

.2 

.2 

0 

1.0 

.8 

—      .2 

i 

Curve  II  ou  Plate  VIII  is  a  graphical  representation  of  tlic  changes  in  the  heating  power  of 
the  sun  on  the  day  of  the  eclipse. 

The  following  table  exhibits  the  observations  with  the  photometer  on  August  7.  The  observa- 
tions ou  July  20  were  made  in  a  similar  manner,  but  only  the  results  are  given  in  Table  IX.  The 
numbers  tabulated  below  indicate  revolutions  of  the  pinion  head,  which,  when  the  aperture  is  open 
o  its  maximum  size,  reads  0.21  rev.,  and  when  completely  closed  reads  1.96  rev. 

TABLE  XI. 


/i.    MI.                              r. 

/(.     HI.                            r. 

1.76 

1.75 

1.82 

1.78 

1.82 

2    30                            1.76 

August  7             11          a.  m.                1.80 

1.72 

1.79 

1.77 

1.76 

1.71 

1.73 

1.70 

1     30  p.  in.              1.  72 

3      0                          1.72    Hazy. 

1.77 

1.  77 

1.76 

1.77 

1.77 

1.74 

1.76 

1.75 

2      0                         1.70 

3     30                            1.74 

1.77 

1.73 

1.80 

1.70 

OBSERVATIONS    OF   THE    ECLIPSE    OP   AUGUST    7,    1809. 
TABLE  XI— Continued. 


119 


• 

/i.    HI.                        r. 

li.    in.                        r. 

1.  75 

1.42 

1.71 

1.42 

3    50                          1.G9 

4     55                          1.44 

1.80 

1.38 

1.78 

1.42 

1.68 

1.59 

1.70 

1.70 

40                          1.67 

5      5                        1.  58 

1.74 

1.64 

1.69 

1.70 

1.68 

1.74 

1.70 

1.74 

4     10                        1.64 

5    15                        1.  69 

1.63 

1.74 

1.69 

1.65 

1.51 

1.64 

1.60    Considerable  increase 

1.67 

4    20                        1.  52  of  cirri  and  haze  over 

5    30                        1.65  Hazy. 

1.57  the  sun. 

1.67 

1.57 

1.60 

1.64 

1.60 

1.67 

1.59 

4    30                        1.63 

5    45                        1.  66  Haze  and  cirri. 

1.66 

1.61 

1.65 

1.68 

1.56 

1.71 

1.50 

1.71 

4    35                        1.54 

60                        1.  70  Quite  clear. 

1.60 

1.69 

1.54 

1.69 

4    46                        "Star"invisihle. 

Variations  in  the  area  of  the  aperture  admitting  light. 

TABLE  XII. 


7i. 

m. 

Area. 

It. 

m. 

Area. 

August  7        11 

0 

0.02 

August  7      4 

20 

.12 

1 

30 

.03 

4 

30 

.06 

2 

0 

.03 

4 

35 

.12 

2 

30 

.03 

4 

55 

.18 

3 

0 

.04 

5 

5 

.12 

3 

30 

.03 

5 

15 

.04 

3 

50 

.03 

5 

30 

.06 

4 

0 

.04 

5 

45 

.07 

4 

10 

.05 

C 

0 

.04 

Using  the  quantities  in  the  above  table  as  linear  ordinates,  the  variation  of  light  on  the  7th 
of  August  may  be  graphically  represented  as  in  the  curve  in  Plate  VIII. 


120 


REPORT    OF   PROFESSOR   EASTMAN. 
TABLE  XIII.— METEOROLOGICAL,  OBSERVATIONS,  AUGUST  7,  1839. 


Maximum  thermometer 
Minimum  thermometer 


Hour. 

Barometer. 

Thermometers. 

Clouds. 

Portion 
cloudy. 

Wind. 

Dry. 

Wet. 

Solar, 

Direction. 

Force. 

h.    m. 

in. 

o 

o 

o 

9      0 

29.  35 

63.8 

59.3 

108.0 

C.  K.  Hazy 

2 

SE. 

3 

10      0 

.33 

67.0 

61.1 

118.0 

C.  K.  Hazy 

2 

SE. 

3 

11      0 

.33 

70.8 

63.0 

122.7 

C.  K.  Hazy 

1 

SE. 

3 

Noou 

.31 

73.0 

64.0 

127.0 

C.  K.  Hazy 

1 

SE. 

2 

1      0 

.31 

73.5 

63.5 

130.5 

C.  K.  Hazy 

1 

SE. 

2 

2      0 

.30 

74.0 

63.8 

127.0 

C.  K.  Hazy 

1 

SE. 

3 

2    30 

.28 

73.3 

63.3 

121.8 

C.  Haze 

1 

SE. 

2 

3      0 

.28 

74.0 

63.5 

119.0 

C.  Haze 

1 

SE. 

2 

3    30 

.27 

74.0 

63.5 

118.5 

C.  Haze 

1 

SE. 

1 

3    50 

.27 

73.0 

63.0 

107.0 

C.  Haze 

t 

SE. 

1 

4    20 

.27 

71.  5 

62.5 

88.8 

C.  Haze 

1 

SE. 

1 

4    30 

.27 

70.5 

62.0 

79.0 

C.  Haze 

1 

SE. 

1 

4     35 

.27 

70.2 

61.7 

75.0 

C.  Haze 

1 

SE. 

1 

4    46 

72.0 

C.  Haze 

1 

SE. 

1 

4    55 

.28 

69.3 

61.5 

68.5 

C.  Haze 

1 

SE. 

2 

r>  so 

.27 

69.5 

61.7 

83.0 

C.  Haze 

0.5 

SE. 

1 

5    40 

.27 

68.9 

62.2 

81.7 

C.  Haze             0.  5 

SE. 

1 

6      0 

.27 

68.8 

61.8 

78.8 

C.  Haze 

1 

SE. 

1 

76°.  0 
53°.  0 


REPORT 


DR.  EDWARD  CURTIS,  U.  S,  A, 


16* 


REPORT    OF    1)11.    EDWARD    CURTIS,    U.    S.    A. 


SURGEON  GENERAL'S  OFFICE, 

Army  Medical  Museum,  Washington,  D.  C.,  November  6,  1869. 

GENERAL:  I  have  the  honor  to  submit  the  following  report  on  the  photographic  observations 
of  the  total  solar  eclipse  of  the  7th  of  August  last,  made  by  the  expedition  from  this  office,  under 
my  charge.  In  response  to  a  request  from  the  Superintendent  of  the  United  States  Naval  Observa- 
tory, accompanied  by  an  offer  of  a  suitable  telescope  and  chronometer,  I  received  on  the  14th  of 
May  last,  through  your  office,  an  order  from  the  War  Department,  directing  me  to  proceed,  in  com- 
pany with  an  astronomical  expedition  from  the  Observatory,  to  Des  Moines,  Iowa,  for  the  purpose 
above  mentioned,  of  taking  photographs  of  the  solar  eclipse.  Hospital  Steward  A.  E.  Le  Merle  and 
Private  M.  S.  Breunan,  United  States  Army,  both  on  duty  in  the  Surgeon  General's  Office,  were 
directed  in  the  same  order  to  accompany  me  as  assistaiits,  and,  in  addition,  the  services  of  Mr.  E. 
J.  Ward,  a  photographer  of  Washington,  were  secured  for  the  occasion. 

I.— SYNOPSIS  OF  OPERATIONS. 

The  members  of  the  party,  leaving  Washington  at  different  dates  early  in  July,  met  at  Chicago 
July  8  and  reached  Des  Moines  July  10.  The  boxes  containing  the  photographic  apparatus,  which 
had  been  previously  expressed  from  Washington  to  Des  Moines,  we  found  awaiting  us  on  our  arrival. 
A  site  for  a  temporary  observatory  was  immediately  selected  near  the  northeastern  limit  of  the  city, 
but,  owing  to  the  incessant  rains  for  a  week  following  our  arrival,  the  erection  of  the  building  was 
so  delayed  that  it  was  not  ready  for  occupation  before  the  20th  instant.  Four  days  were  then  con- 
sumed in  unpacking  the  boxes,  mounting  the  telescope,  fitting  up  the  dark-room,  and  preparing  the 
chemicals  for  use.  'On  the  24th  of  July  the  first  sun  picture  was  taken,  and  from  this  date  until 
the  7th  of  August  every  fair  afternoon  was  spent  in  experimenting  and  practicing  with  our  instru- 
ment. Of  the  negatives  obtained  on  the  2Gth  and  subsequent  days  one  from  each  day's  work  has 
been  kept  as  a  record  of  the  appearance  of  sun-spots.  On  the  7th  of  August  six  negatives  of  the 
sun,  of  which  also  one  has  been  preserved,  were  taken  early  in  the  afternoon  for  the  purpose  of 
testing  the  condition  of  the  chemicals,  and  on  the  occasion  of  the  eclipse  one  hundred  and  twenty- 
two  exposures  were  made,  as  follows:  two  immediately  before  the  time  of  first  contact,  fifty-nine 
during  the  partial  phase  between  the  periods  of  first  contact  and  the  commencement  of  totality, 
two  during  the  total  obscuration,  fifty-seven  between  the  times  of  reappearance  of  the  sun  and  last 
contact,  and  two  immediately  after  the  latter  event.  Of  these  negatives  three  of  the  partial  phase 
following  totality  were  spoiled,  leaving  a  total  of  one  hundred  and  nineteen  plates  actually  secured. 
One  negative  of  the  sun  was  also  taken  each  afternoon  for  two  days  following  the  eclipse— days 
that  were  spent  in  varnishing  and  packing  the  negatives  and  precipitating  the  silver  baths  for 
transportation.  Two  more  days  were  consumed  in  dismantling  the  observatory  and  packing  up  for 
departure,  and  on  the  12th  of  August  the  expedition  started  on  its  return. 

In  connection  with  the  solar  photography  a  series  of  experiments  was  also  instituted  to  deter- 
mine photographically  the  relative  amount  of  actinic  force  exerted  by  the  sun  at  different  altitudes. 
These  experiments  -were  made  on  eight  separate  days,  and  comprise  seventy-nine  photographic  tests 
of  the  sun's  chemical  power. 

Stereoscopic  and  other  views  of  the  observatory  and  neighboring  scenery,  the  instruments,  and 
members  of  the  expedition  at  their  various  duties,  were  also  taken  at  odd  moments  by  Messrs.  Le 
Merle  and  Ward. 


124  REPORT   OF   DR.    CURTIS. 

To  sum  up,  the  material  results  of  the  photographic  expedition  arc  as  follows:  eleven  negatives 
of  the  sun,  representing  the  appearance  of  that  body  on  as  many  different  days;  one  hundred  and 
nineteen  negatives  of  the  solar  eclipse  of  August  7;  seventy-nine  photographic  paper  slips  showing 
the  relative  actinic  force  of  the  sun  at  different  altitudes  on  eight  separate  days;  twenty- three 
stereoscopic  and  other  negatives. 

In  accordance  with  your  instructions,  the  eclipse  negatives  will  be  placed  at  the  disposal  of  the 
Superintendent  of  the  Naval  Observatory  for  the  reading  off  of  the  astronomical  information  which 
they  contain.  On  the  completion  of  this  work  they  will  be  deposited,  with  the  other  results  of  the 
expedition,  in  the  Army  Medical  Museum. 

The  following  is  a  detailed  description  of  the  apparatus  and  methods  of  procedure  followed  in 
the  photographic  work,  an  account  in  full  of  our  operations,  and  a  discussion  of  the  results  obtained : 

II.— THE  TELESCOPE. 

The  telescope  used  was  the  large  equatorial  of  the  United  .States  Naval  Academy,  at  Annapolis, 
Maryland,  which  was  loaned  to  the  Naval  Observatory  for  the  expedition,  at  the  request  of  Commo- 
dore Sands,  by  Vice-Admiral  I).  D.  Porter,  United  States  Navy,  superintendent  of  the  Academy. 
This  instrument  is  a  refractor,  constructed  by  Alvau  Clark  &  Sons,  of  Cambridge  port,  Massachusetts, 
in  1857.  It  has  an  object-glass  of  7.75  inches  clear  aperture  and  nine,  feet  six  inches  local  length. 
The  tube  is  mounted  eqnatorially,  in  the  German  style,  on  a  solid  cast  iron  pier,  provided  with  a 
spring- governor  driving  clock.  The  tinder  of  the  instrument  is  a  small  telescope,  with  an  object 
glass  of  1.7  inches  clear  aperture  and  20.25  inches  focal  length. 

This  telescope,  having  been  received  at  the  Naval  Observatory  in  Washington  in  .May,  was 
mounted  temporarily  in  a  wooden  shed  on  the,  grounds  of  that  institution,  .and  there  fitted  up  for 
photographic  use.  For  this  purpose  the,  following  apparatus  had  to  be  made: 

1.  A  heavy  wooden  cross  for  the  pier  of  the  telescope  to  rest  upon. 

2.  A  camera-box  to  be  attached  to  the  eye  end  of  the  instrument  and  fitted  up  with  two  differ- 
ent arrangements  for  making  the  exposures,  one  to  be  used  during  the  total  and  the  other  during 
the  partial  phases  of  the,  eclipse. 

3.  A  diaphragm  carrying  two  position  wires  crossing  at  right  angles,  to  be  adjusted  in  the  eye- 
piece. 

4.  A  clamp  to  hold  the  eye-piece  immovable  in  its  tube  after  adjustments  for  focus  and  angle 
of  the  position  wires. 

5.  Diaphragm  caps  of  different  sizes  to  reduce  the  aperture,  of  the  object-glass  in  photographing 
the  partial  phases  of  the  eclipse. 

C.  New  weights  for  the  driving  clock,  the  old  ones  being  too  long  to  use  conveniently. 

7.  A  new  suspension-piece  for  the  pendulum  of  the  clock  to  rest  upon.  This  change  was  required 
from  the  fact  that,  there  being  no  arrangement  for  altering  the  position  of  the  polar  axis,  the  pier 
itself  had  to  be  tipped  up  to  make  allowance  for  the  difference  in  latitude  between  DCS  Moines  and 
Annapolis.  A  new  suspension-piece  was  therefore  needed  for  the  pendulum,  to  suit  the  altered 
position  of  the  pier. 

All  these  additions  to  the  telescope  were  made  under  the  immediate  supervision  of  Professor 
William  Harkness,  United  States  Navy,  the  brass  work  being  done  by  Mr.  W.  F.  Gardner,  instru- 
ment maker  at  the  Observatory,  who  worked  most  zealously  that  everything  might  be  completed  in 
amide  time  for  an  early  departure  for  the  West.  Four  plate-holders  and  a  frame  carrying  a  ground- 
glass  screen  were  also  prepared  under  my  own  direction. 

The  camera-box  requires  special  description.  In  devising  this  piece  of  apparatus  the  first  ques- 
tion that  presented  itself  was  whether  to  use  the  focal  image  of  the  object-glass  alone  to  produce 
the  sun-pictures  or  to  enlarge  it  by  the  interposition  of  a  Huyghenian  eye-piece.  The  answer  was 
emphatically  given  in  favor  of  the  latter  plan,  for  the  following  reasons :  In  the  first  place,  it  could 
only  be  by  means  of  an  eye-piece  that  position  ^ires  could  be  used  and  depicted  upon  the  plates, 
and  without  these  the  value  of  the  negatives  of  the  partial  phases  for  astronomical  purposes  would 
be  greatly  impaired ;  in  the  second  place,  a  fair  size  for  the  sun-pictures  was  considered  an  important 
consideration— in  the  partial-phase  negatives  as  conducing  to  greater  accuracy  in  the  niicrometrical 


1869.  125 

measurements,  and  iii  those  of  the  totality  as  giving  such  dimensions  to  the  red  protuberances  that 
points  of  structure  and  detail  iu  those  bodies  might  bo  caught  and  recognized  without  the  necessity 
of  subsequent  enlargement  of  the  negative,  an  operation  that,  iu  my  judgment,  is  always  to  be 
avoided.  The  only  drawback  to  the  use  of  an  eye-piece  was  the  comparatively  long  exposures 
required  in  consequence  during  totality,  making  it  possible  to  obtain  but  few  photographs  of  that 
phase ;  but  I  considered  that  even  one  negative,  showing  the  structure  of  the  red  prominences  ou 
a  comparatively  large  scale,  would  be  worth  a  dozen  little  images  where  nothing  but  the  mere  posi- 
tion of  the  principal  protuberances  could  hope  to  be  shown. 

It  was  therefore  decided  to  use  an  eye-piece,  to  employ  negative  plates  seven  inches  square,  and 
to  place  them  at  such  a  distance  from,  the  eye-piece  that  the  image  of  the  sun  projected  upon  them 
should  be  as  nearly  as  possible  four  inches  in  diameter.  To  meet  these  requirements  a  long  slightly - 
lapering  camera  bo.v,  with  square  ends,  was  constructed.  This  was  made  in  two  parts,  the  joint 
running  lengthwise,  with  the  smaller  end  fitted  to  clasp  the  telescope  tube  tightly  around  its  entire 
circumference  at  two  places  eleven  inches  apart,  wheu  the  two  halves  of  the  box  were  screwed 
together  upon  the  instrument.  This  fastening  was  accomplished  by  stove-bolts  passing  through 
solid  lugs  of  wood  which  projected  from  the  sides  of  the  box  along  the  line  of  junction  of  the  two 
halves.  The  posterior  or  free  end  of  the  camera  was  fitted  to  allow  the  plateholder  to  slide  in  upon 
a  slip  of  glass  let  into  the  wood,  the  holder  being  then  held  in  position  by  the  pressure  of  two  strong 
brass  springs  from  behind.  The  various  uprights  of  the  framework  at  this  end  of  the  box  were  so 
made  that  in  all  cases  two  projecting  arms  from  each  half  of  the  box  should,  when  the  latter  were 
fitted  together,  slide  past  each  other  so  as  to  admit  of  being  screwed  into  one  piece,  thus  making 
the  framework  solid  and  light-tight.  The  arrangement  for  making  the  exposures  was  as  follows: 
About  two  and  a  half  inches  beyond  the  end  of  the  eye-piece  was  a  fixed  partition  across  the 
camera  box,  pierced  with  a  central  aperture  just  large  enough  to  admit  the  entire  cone  of  rays  from 
the  instrument.  Immediately  in  front  of  this,  passing  through  rebated  slots  in  the  sides  of  the 
camera  box,  was  a  movable  wooden  slider  long  enough  to  project  several  inches  beyond  the  sides  of 
the  camera,  and  pierced  with  two  apertures,  either  of  which  could  be  centered  with  the  hole  in  the 
fixed  partition  by  simply  running  the  slider  to  or  fro  a  few  inches.  In  either  position  of  the  slider 
it  was  held  in  place  by  a  spring  bolt  on  the  side  of  the  camera.  One  of  these  apertures — for  use 
during  totality — was  fitted  up  with  a  light  brass  shield  turning  laterally  on  a  pivot,  by  means  of 
which  the  hole  could  be  covered  or  uncovered,  the  shield  being  operated  from  without  by  being 
attached  by  a  catgut  cord  to  a  little  cylinder  surmounted  by  a  milled  head  fixed  at  the  free  pro- 
jecting end  of  the  slider.  A  stop  was  originally  provided  to  limit  the  swing  of  the  shield  when 
thrown  aside  to  expose  the  aperture  beneath,  but,  finding  that  the  striking  of  the  shield  upon  it 
produced  a  sensible  jarring  of  the  telescope,  the  stop  was  removed.  The  other  aperture — to  allow 
of  instantaneous  exposures  during  the  partial  phases — was  covered  by  a  rectangular  brass  plate 
running  freely  on  guide-rods  and  pierced  with  a  transverse  slot  half  an  inch  in  width,  which  was 
adjustable  to  a  slit  of  any  dimensions  by  means  of  a  secondary  slotted  plate,  attached  to  the  first 
by  screws.  Instantaneous  motion  of  this  plate  across  the  aperture  was  effected  by  a  fine  steel  wire 
spring  coiled  around  one  of  the  guide-rods;  and  when  drawn  up  against  the  spring  the  plate  was 
held  by  a  wire  loop  catching  over  a  little  pin  which  projected  upwards  through  a  bridge  from  the 
upper  surface  of  a  spring  trigger,  also  placed  at  the  free  end  of  the  slider.  A  light  touch  upon  this 
trigger  then  released  the  plate,  when  the  rapid  flashing  of  the  slit  across  the  aperture  in  the  slider 
effected  the  exposure;  and  by  pressing  the  trigger  always  at  a  predetermined  second  of  time,  with 
eye  and  car  upon  a  chronometer  standing  close  by,  the  timing  of  the  exposures  could  be  made  with 
the  utmost  accuracy.  The  accompanying  figure  represents  the  wooden  slider,  fitted,  as  described, 
with  the  apparatus  for  making  the  exposures. 


126 


REPORT   OF    DR.    CURTIS. 


The  tube  of  the  telescope  being  adjusted  to  the  position  it  would  occupy  during  the  eclipse,  tlu> 
camera  box  was  clamped  upon  it  in  such  a  manner  that  the  plateholdcrs  and  the  wooden  slider  should 
run  in  from  the  side  with  the  lower  edges  maintained  horizontal.  On  the  top  of  the  camera  box  as 
thus  placed  the  finder  of  the  telescope  was  mounted.  At  a  suitable  distance  behind  it  was  an 
upriglt  of  wood  carrying  a  slip  of  ground  glass  with  a  circle  drawn  on  it,  to  serve  as  a  screen  on 
which  to  view  the  image  of  the  sun  from  the  finder  when  adjusting  the  telescope.  To  provide  for 
the  fainter  image  of  the  corona  during  totality,  a  movable  screen  of  white  card-board  was  made  to 
slip  over  the  ground  glass,  so  as  to  give  a  more  brilliant  surface  for  the  reception  of  the  image.  On 
this  also  a  circle  was  drawn  to  center  the  image  by.  In  the  under  face  of  the  camera  box  a  door 
was  cut  to  permit  the  hand  to  reach  the  eye-piece,  in  adjusting  the  latter  for  focus  and  angle  of  the 
position  wires. 

The  accompanying  woodcut,  from  a  photograph  by  Mr.  Le  Merle,  shows  the  telescope  as  it 
appeared  when  in  actual  use  in  the  afternoon.  The  chronometer  is  seen  strapped  to  a  tripod  stand 
close  to  the  camera  box,  and  the  operator  is  represented  in  the  act  of  timing  an  exposure,  the  end 
of  the  slider  carrying  the  trigger  being  beliiud  the  camera,  and  therefore  not  seen  in  the  cut. 


OBSERVATIONS   OP   THE   ECLIPSE    OP   AUGUST   7,    1869.  127 

III.— THE  OBSERVATORY. 

A  site  for  a  joint  temporary  observatory  at  Des  Moiues,  to  serve  both  for  my  owu  party  and 
for  Professors  Harkuess  and  Eastman,  was  selected  on  a  piece  of  high  ground  at  the  northern 
limit  of  Second  street.  This  offered  the  advantages  of  as  close  an  approach  to  the  central  line  of 
the  eclipse  as  possible,  a  clear  horizon  in  all  directions,  a  well  of  good  water  close  by,  freedom 
from  dust,  and  good  drainage.  The  exact  position  occupied  by  the  photographic  equatorial,  as 
determined  by  Professor  Harkness,  is  as  follows:  latitude,  41°  35'  36";  longitude,  Iu6m16s.05 
west  of  center  of  dome  of  United  States  Naval  Observatory  at  Washington ;  height  above  the 
level  of  the  sea,  831  feet. 

On  this  site  a  rough  board  building  thirty-two  by  sixteen  feet  was  erected,  running  nearly  north 
and  south  in  the  direction  of  its  length.  The  entire  building  was  floored,  and  from  the  northern 
end  an  extent  of  seven  feet  was  partitioned  off  for  the  dark-room  and  ceiled  on  a  level  with  the 
eaves.  The  remainder  of.  the  building  was  one  large  room,  with  the  western  slope  of  the  roof  and 
upper  portion  of  the  western  wall  not  boarded,  but  covered  by  a  canvas  roof  which  could  be  rolled 
up  when  the  telescopes  were  to  be  iised. 

The  dark-room  was  furnished  with  seven  negative  baths,  standing  in  a  long  trough  filled  with 
water  to  keep  them  cool,  a  sink  composed  of  a  common  wash-tub  with  an  India-rubber  waste-pipe 
attached,  a  barrel  of  water  standing  on  a  platform  outside  the  building  with  a  pipe  closed  by  a 
stop-cock  projecting  through  the  wall,  and  a  large  flxing-bath  composed  of  a  wooden  trough  with 
grooved  sides  like  a  negative  rack,  capable  of  holding  one  hundred  and  fifty  plates  and  filled  with 
a  very  weak  solution  of  hyposulphite  of  soda.  The  room  was  provided  with  ventilators  on  a  level 
with  the  floor  and  in  the  ceiling,  and  in  the  partition  wall  adjoining  where  the  telescope  stood 
were  two  little  dumb-waiters  by  which  the  plate-holders  could  be  passed  in  and  out  of  the  dark- 
room without  the  admission  of  light  or  the  necessity  of  any  of  the  operators  moving  from  their 
places.  Plate  I,  from  a  photograph  by  Mr.  Ward,  gives  a  view  of  the  observatory  with  the  canvas 
roof  rolled  up  and  the  telescopes  ready  for  use,  and  Plate  II,  from  a  drawing  by  Mr.  Le  Merle, 
shows  the  arrangement  of  parts. 

IV.— PRELIMINARY  EXPERIMENTS. 

The  telescope  being  ready  for  use  in  June,  we  immediately  commenced  our  self-taught  lessons 
in  celestial  photography.  These  preliminary  experiments,  commenced  in  Washington,  were  con- 
tinued after  our  arrival  in  Des  Moines,  and  were  for  the  purpose  of  determining  the  chemical 
focus  of  the  optical  combination,  selecting  the  most  suitable  photographic  formula;  for  the  special 
work,  studying  the  subject  of  lengths  of  exposure  both  for  the  partial  phases  and  for  totality, 
deciding  upon  a  plan  of  operations  to  be  followed  during  the  eclipse,  and  drilling  ourselves  thor- 
oughly in  our  respective  duties,  so  that  there,  might  be -no  mistake  or  contretemps  at  the  critical 
moment. 

1.  Determination  of  the  chemical  focus. — I  confess  to  having  had  a  great  deal  of  anxiety  about 
the  photographic  performance  of  the  telescope,  both  on  account  of  the  object-glass  being  an  ordi- 
nary achromatic  lens  not  corrected  for  photography  and  on  the  score  of  the  additional  confusion 
that  must  arise  from  the  use  of  an  eye-piece.  I  was  fearful  that  with  such  a  combination  no 
adjustment  of  the  focus  would  give  a  picture  sufficiently  sharp  for  exact  micrometrical  measure- 
ment. The  first  day's  trial,  however,  removed  my  doubts,  for  with  a  two-inch  diaphragm  cap  over 
the  object-glass  the  sun  picture  came  up  beautifully  sharp  as  soon  as  the  chemical  focus  was 
found.  This  focus  was  determined  experimentally  by  sliding  the  eye-piece  to  and  fro  until  the 
best  photographic  effect  was  produced.  And  since  the  curvature  of  field  affected  slightly  the 
definition  at  different  distances  from  the  center  of  the  plate,  that  position  of  the  eye-piece  was 
selected,  in  order  to  secure  the  best  mean  focus,  which  should  give  the  sharpest  definition  midway 
.  between  the  center  and  limb  of  the  sun's  image.  Using,  then,  as  a  test  object,  a  large  sun-spot 
that  happened  to  occupy  just  this  position  on  the  solar  disk,  the  proper  adjustment  of  the  eye- 
piece for  the  required  focus  was  determined  with  great  care  and  recorded.  But  this  determination 
being  made  with  a  two-inch  diaphragm  cap  over  the  object-glass,  it  was  necessary  to  test  also  the 
performance  of  the  full  aperture  of  the  lens  with  the  same  focus,  since  this  aperture  would  be  used 


128  REPORT   OF   DR.    CURTIS. 

during  totality.  For  this  purpose  solar  negatives  were  taken  .just  before  sunset,  when  the  feeble 
actinic  force  of  the  sun  permitted  the  whole  diameter  of  the  object-glass  to  be  used  without  over- 
exposure  of  the  plates,  and  it  was  found  that  with  this  aperture  the  definition  was  not  nearly  so 
good  as  when  the  two-inch  diaphragm  cap  was  employed,  but  that  the  focus  could  not  be  improved. 
2.  Selection  of  photographic  formula. — In  deciding  upon  what  formulae  for  bath,  collodion,  and 
developer  to  use  during  the  eclipse,  regard  was  had  exclusively  to  the  peculiar  phenomena  of  total- 
ity, since  the  sun  negatives  during  the  partial  phases,  intended  solely  for  micrometrical  measure 
uient,  could  be  obtained  equally  well  by  any  process.  The  subject  presented  peculiar  difficulties, 
since  it  involved  representing  upon  one  plate,  if  possible,  the  corona,  possessing  very  feeble  actinic 
power,  and  the  red  protuberances,  which,  on  the  contrary,  exert  a  very  strong  photographic  action. 
Desirous  of  knowing  how  far  this  difficulty  had  been  overcome  by  previous  operators,  I  obtained 
copies  of  Dr.  Vogel's  photographs  of  the  eclipse  of  1868  in  Arabia,  and  through  the  kindness  of 
my  friend,  Dr.  R.  L.  Maddox,  of  Southampton,  England,  and  the  courtesy  of  Mr.  Richard  Beck,  of 
London,  was  also  furnished  with  prints  of  Mr.  De  La  Rue's  negatives  of  the  totality  in  the  eclipse 
of  1860  in  Spain.  In  both  cases  the  prints  were  from  enlarged  negatives,  which  was  to  be 
regretted,  for  in  such  pictures  much  of  the  detail  of  the  original  negative  is  infallibly  lost.  An 
examination  of  these  prints  showed  in  the  photographs  of  De  La  Rue  a  very  faint  corona,  with 
the  prominences  nevertheless  so  dense  that  but  little  detail  in  them  could  be  made  out.  The 
Arabian  pictures  presented  the  same  characteristics  still  more  strongly  marked,  the  corona  being 
scarcely  visible  at  all,  while  the  red  protuberances  appeared  as  mere  masses  of  white  upon  a  black 
ground.  In  the  latter  instance  much  of  the  effect  described  may  have  been  due  to  bad  weather; 
still  I  could  not  help  believing  that  in  both  cases  collodions  had  been  used  that  gave  brilliant  pic- 
tures of  great  intensity  rather  than  soft  negatives  full  of  detail,  and  that,  by  a  selection  of  chemi- 
cals that  should  produce  the  latter  effect  rather  than  the  former,  much  better  results  might  be 
obtained.  The  subject  was  fully  discussed  with  Mr.  Le  Merle,  a  practical  photographer  of  long 
experience,  to  whom  the  preparation  of  the  chemicals  was  intrusted,  and  he,  entertaining  the  same 
views,  felt  confident  that  with  a  collodion  of  his  own,  containing  a  full  proportion  of  bromide,  a 
sufficient  exposure,  and  careful  development  with  a  moderately  strong  developer,  negatives  could 
be  secured  that  would  show  detail  in  the  prominences  and  give  a  fair  indication  of  the  corona  as 
well.  Accordingly  he  prepared  his  solutions  by  the  following  formulae: 

COLLODION. 

Iodide  of  ammonium  .">  grains. 

Iodide  of  cadmium  5  grains. 

Bromide  of  cadmium  5  grains. 

Atxvood's  alcohol,  95  per  cent.  1  fluid  ounce. 

Sulphuric  ether  1  fluid  ounce. 

Pyroxyline,  (Anthony's  negative,)  enough  to  give  the  proper  consistency. 
The  collodion  intended  for  use  during  the  eclipse  was  made  in  a  large  stock  bottle  on  the  29th 
of  July,  and  on  the  fifth  of  August  was  brought  to  a  lemon  yellow  color  by  addition  of  tincture  of 
iodine. 

BATH. 

Nitrate  of  silver,  recrystallized   -  40  grains. 

Distilled  water      -  1  fluid  ounce. 

Nitric  acid,  C.  P.,  sufficient  to  make  the  bath  work  clean  under  a  long  development 
with  the  above  collodion. 

The  bath  solution  was  made  five  days  before  the  eclipse,  was  dosed  with  the  proper  amount  of 
iodide  of  silver  in  the  usual  way,  and  was  worked  a  little  each  day. 

DEVELOPER. 

Saturated  solution  of  sulphate  of  iron  1  £  fluid  ounces. 

Acetic  acid,  No.  8  1£  fluid  ounces. 

Water ...  13  fluid  ounces. 


OBSERVATIONS    OF   THE    ECLIPSE    OF   AUGUST   7,    1869.  129 

The  delicate  beauty  of  the  totality  negatives  obtained,  which,  while  showing  considerable  of 
the  corona,  are  full  of  detail  in  the  prominences,  proves  the  soundness  of  the  views  entertained  and 
the  excellency  of  Mr.  Le  Merle's  formula'  for  producing  the  desired  result. 

3.  Estimation  of  the  length  of  exposures.— The  exposure  during  the  partial  phases  was  simply  a 
matter  to  be  decided  by  direct  experiment  upon  the  sun,  and  it  was  found  that  while  a  two-inch 
aperture  to  the  object-glass  gave  abundant  exposure  in  the  middle  of  the  day,  this  had  to  be  some- 
what increased  as  the  afternoon,  advanced  and  the  sun  approached  the  horizon.  The  width  of  the 
slit  in  the  instantaneous  plate  found  necessary  varied  from  a  quarter  to  half  an  inch,  but  while  this 
may  seem  excessive,  it  must  be  remembered  that  the  plate  was  about  an  inch  and  a  half  from  the 
eye-piece. 

The  question  of  the  length  of  exposure  to  be  given  to  the  plates  during  totality,  was,  on  account 
of  its  great  importance,  made  the  subject  of  careful  study  and  experiment.  As  a  basis  for  this  esti- 
mation I  determined  to  rely  exclusively  on  the  teachings  of  De  La  Eue's  totality  pictures  of  the  1860 
eclipse,  considering  these  as  the  most  satisfactory  photographs  of  the  phenomenon  in  existence. 
This  astronomer's  result  afforded  two  ways  of  making  the  estimate.  The  first  depended  upon  his 
calculation  of  the  relative  photographic  intensity  of  the  light  from  the  red  prominences  and  full 
moon.  This  calculation  he  made  as  follows  :  *  During  the  taking  of  his  second  totality  picture  the 
telescope  was  shaken  and  three  impressions  of  the  prominences  appeared.  From  their  relative 
intensity  he  inferred  that  the  faintest  of  these  received  twelve  seconds'  exposure.  Attempting  to 
photograph  the  full  moon  with  the  same  instrument  used  for  the  eclipse  he  obtained  an  "  extremely 
faint  impression"  after  an  exposure  of  three  minutes.  This  impression  he  estimated  to  be  one- 
twelfth  the  intensity  of  the  faintest  of  the  impressions  of  the  prominences  above  referred  to,  an  esti: 
mate  which  makes  the  relative  photographic  power  of  the  full  moon  and  solar  prominences  as  180 
to  1.  Taking  this  estimate  for  what  it  was  worth,  and  inferring  (though  De  La  Eue  does  not  so 
state)  that  he  photographed  the  full  moon  when  at  nearly  the  same  altitude  as  the  sun  during  the 
1860  eclipse,  I  determined  to  try  the  full  moon  with  my  own  telescope  and  see  what  length  of  expo- 
sure would  be  necessary  to  produce  a  fair  impression  of  that  satellite  when  at  an  altitude  of  about 
26°,  the  position  that  the  totally  eclipsed  sun  would  occupy  on  the  7th  of  August.  Dividing  this 
time  by  180  should  then  give  the  time  necessary  to  produce  a  correspondingly  strong  impression  of 
the  prominences.  The  full  moon  occurred  at  8h  30m  p.  m.,  Washington  mean  time,  on  the  23d  of 
June,  but  that  evening  was  unfortunately  cloudy,  so  that  the  experiment  could  not  be  made  till  the 
following  night,  when  the  moon  of  course  was  many  hours  past  the  full.  It  was  then  found  that  at 
26°  above  the  horizon  five  minutes  produced  a  weak  image,  ten  and  fifteen  a  better,  and  twenty  an 
image  that  came  up  promptly  under  the  developer.  But  since  there  was  no  means  of  allowing  for 
the  moon's  motion  in  declination  during  these  long  exposures,  the  pictures  were  necessarily  mere 
blurs,  and  it  was  very  difficult  to  say  exactly  what  was  the  correct  exposure.  Moreover,  when  it 
came  to  an  exposure  of  twenty  minutes,  five  minutes  more  or  less  seemed  not  to  make  any  great 
difference  in  the  strength  of  the  image.  These  experiments  were  therefore  exceedingly  unsatisfac- 
tory ;  and  considering  also  that  De  La  line's  original  calculation  of  the  comparative  actinic  force,  of 
the  light  of  the  moon  and  the  red  flames  was,  though  the  best  that  could  be  made,  yet  necessarily 
rather  loose,  I  determined  to  abandon  altogether  this  method  of  estimating  the  totality  exposures 
as  untrustworthy,  and  to  rely  exclusively  upon  the  second  method  afforded  by  De  La  Rue's  labors, 
that,  namely,  of  calculating  directly  from  the  exposures  he  gave  his  own  totality  pictures  in  Spain. 
This  was  a  very  simple  matter.  In  the  first  place,  I  proposed  to  follow  his  plan  of  using  an  eye-piece 
to  magnify  the  focal  image  of  the  object-glass,  and  moreover  to  represent  the  sun  upon  the  photo- 
graph of  the  same  size  as  in  his  pictures.  So  far  as  the  telescopes  were  concerned,  therefore,  the 
exposures  to  produce  like  effects  should  be  exactly  proportional  to  the  size  of  the  instruments;  that 
is,  inversely  as  the  areas  of  the  object-glasses.  Now,  the  object-glass  of  the  Kew  photo-heliograph 
is  3.4  inches  in  diameter,  that  of  the  Annapolis  equatorial  7.7/5  inches ;  or,  in  other  words,  taking  the 
proportion  of  the  squares  of  these  diameters,  my  equivalent  exposure  should  be  slightly  less  than  one- 
fifth  that  of  De  La  Eue.  An  exposure,  that  is,  of  eleven  and  a  half  seconds  with  my  telescope  should, 
other  things  being  equal,  produce  the  same  result  as  the  one-minute  exposure  given  by  De  La  Eue. 
I  say  "  other  things  being  equal,"  because  an  important  consideration  has  been  disregarded  in  stating 

'  I'liilosopliiriil  Transactions,  18(52,  l>ag«'  405. 


130  REPORT    OF   DR.    CURTIS. 

this  estimate,  namely,  the  effect  oil  the  necessary  length  of  exposure  of  the  dilfereut  altitude  of  the 
sun  on  the  occasion  of  the  two  eclipses.  In  De  La  Hue's  case  the  sun  was  near  the  zenith,  whereas 
in  the  1869  eclipse  it  would  be  but  26°  above  the  horizon.  In  proportion,  therefore,  to  the  sun's 
loss  of  actinic  force  when  at  this  altitude  the  estimated  exposure  for  the  totality  whould  have  to  be 
increased.  In  order  to  determine  exactly  what  this  loss  was  I  began  experimenting  by  testing  the 
length  of  exposure  necessary  to  produce  negatives  of  the  sun  of  equal  intensity  at  mid-day  and  at 
a  quarter  to  five  in  the  afternoon.  But  owing  to  the  latitude  that  always  exists  in  exposures  of 
negatives  by  the  wet  collodion  process,  I  soon  abandoned  this  method  as  too  coarse  and  uncertain, 
and  resorted  to  comparative  exposures  of  photographic  paper.  These  were  made  in  the  following 
way :  A  strip  of  sensitized  paper  was  tacked  to  a  board  and  covered  by  a  sheet  of  yellow  paper  in 
which  were  cut  out  twenty-seven  rectangular  spaces.  The  board,  covered  by  a  velvet  cloth,  was 
set  up  so  as  to  exactly  face  the  sun,  when  at  a  given  second,  timed  by  the  chronometer,  the  vel- 
vet was  whisked  away,  and  by  means  of  narrow  strips  of  wood  the  rectangular  spaces  were  suc- 
cessively and  suddenly  covered  over  at  definite  periods  of  time,  thus  effecting  a  different  length  of 
exposure  for  the  sensitive  paper  under  each  space.  Such  a  series  of  exposures  was  made  at  differ- 
ent hours  of  the  day,  the  times  of  exposure  being  invariably  the  same.  These  times  were  as  fol- 
lows, the  numbers  meaning  seconds :  £,  1, 2,  3,  4,  5,  7J,  10,  12i,  15,  17J,  20,  25,  30,  35,  40,  50,  60 ; 
and  also,  when  the  light  was  feeble,  80, 110, 150,  200,  260,  330,  410,  500,  600.  Then  by  taking  the 
slip  exposed  at  noon  as  a  standard,  and  matching  shades  with  those  exposed  at  other  hours,  the 
relative  amount  of  actinic  action  exerted  by  the  sun  was  roughly  calculable.  That  is,  if  at  5h  p.  in., 
for  instance,  the  space  exposed  for  ten  seconds  is  identical  in  shade  with  that  exposed  for  five  sec- 
onds at  noon,  and  if  the  proportion  holds  good  in  the  other  spaces,  the  reasoning  is  that  at  that 
hour  the  sun's  actinic  force,  as  measured  by  the  photographic  effect  produced,  is  one-half  that  at 
noon.  But  not  to  rely  upon  any  single  comparison,  the  shades  in  any  one  slip.were,  in  all  cases  that 
would  admit  of  it,  matched  at  least  as  high  as  the  shade  produced  by  an  exposure  of  fifty  or  sixty 
seconds,  and  the  mean  of  the  results  obtained  from  these  various  comparisons  was  taken  as  the 
expression  of  the  sun's  chemical  power  at  the  time.* 

*  It  is  proper  to  state  that  neither  at  the  time  of  making  these  experiments  nor  of  writing  the  above  had  I  read  of 
Professor  Roscoe's  critical  observations  of  this  character  at  Manchester,  England,  (I'hil.  Trans.,  1863,  p.  139,  and  1865, 
p.  605.)  It  will  be  seen  that  my  own  was  a  rough  method  of  applying  the  same  principles  as  those  involved  in  Profes- 
sor Roscoe's  elaborate  and  admirable  arrangement.  The  question  as  to  the  relation  between  length  of  exposure  and  chemi- 
cal intensity  of  light  in  producing  identical  shades  of  blackening  I  had  also  experimented  upon,  in  order  properly  to 
interpret  the  results  of  the  photo-chemical  observations,  and  had  reached  the  same  conclusions  that  Professors  Bunseu 
and  Roscoe  had  previously  arrived  at,  nnconsciously  verifying,  by  a  different  experiment,  the  law  of  this  relation  dis- 
covered by  them  and  thus  announced:  (Phil.  Trans.,  1863,  p.  145.)  "  Equal  products  of  the  intensity  of  the  light  into 
the  time  of  insolation  correspond,  within  very  wide  limits,  to  equal  shades  of  darkness  produced  on  chloride-of-silvcr 
paper  of  uniform  sensitiveness."  My  plan  of  experimenting  on  this  subject  was  rough  and  simple,  like  that  of  the  other 
actinometrical  observations,  but  quite  effective.  A  sensitized  paper  strip  was  first  exposed  at  noon  in  the  precise  man- 
ner described  above  in  the  text,  different  spaces  on  the  strip  receiving  different,  lengths  of  exposure,  and  care  being  taken 
that  the  surface  of  the  paper  should  be  exactly  at  right  angles  to  the  course  of  the  solar  beam.  Immediately  afterwards 
a  second  strip  was  exposed,  the  board  to  which  it  was  tacked  being,  in  this  case,  inclined  to  the  direction  of  the  sun's 
rays  at  such  an  angle  that  the  shadow  of  a  strip  of  cardboard  projecting  from  the  face  of  a  box  previously  carefully 
adjusted  so  as  to  exactly  face  the  sun,  should,  when  falling  from  the  board  immediately  under  it,  measure  twice  the 
actual  width  of  the  cardboard  itself.  Under  these  circumstances  each  space  of  this  sensitized  strip  received,  of  course, 
but  one-half  the  amount  of  sunlight  that  impinged  upon  those  of  the  first  strip,  and  a  comparison  of  the  two  strips 
showed  that  in  all  cases  double  the  length  of  exposure  was  required  on  the  second  strip  to  produce  degrees  of  blacken- 
ing identical  with  the  shades  of  the  first. 

The  actinometrical  experiments  described  in  the  text,  -which  were  undertaken,  as  then1  stated,  for  the  purpose  of 
estimating  the  length  of  the  totality  exposures,  led  me,  by  their  interest,  into  making  something  of  a  series  of  them  in 
order  to  test,  approximately,  the  chemical  force  of  the  sun  at  all  altitudes.  One  day,  the  29th  of  July,  was  entirely 
given  up  to  this  work,  and  photographic  observations  were  taken  from  sunrise  to  sunset  at  every  fifteen  minutes  during 
the  morning  and  afternoon,  and  every  half  and  whole  hour  during  the  middle  of  the  day.  Although  from  the  compara- 
tively rude  character  of  the  method  of  observation  the  results  obtained  can  only  be  considered  as  rough  approximations 
to  the  truth,  yet  they  are  sufficiently  accurate  for  the  purposes  of  a  practical  photographer  in  estimating  lengths  of 
exposure  for  negatives,  and  possess,  it  is  believed,  so  far  as  they  go,  a  peculiar  value  on  account  of  the  unusually  cloud- 
less skies  and  equable  condition  of  the  atmosphere  in  that  splendid  Iowa  climate  during  the  period  through  which  the 
observations  extended.  A  table  of  the  results  of  the  observations  is  accordingly  given  in  Schedule  B.  Though  for  the 
sake  of  avoiding  error  as  far  as  possible  the  slips  of  each  day  were  invariably  compared  with  the  noon  shade  of  the  same 
day  as  the  standard,  yet  these  mid-day  slips  have  been  found  to  differ  so  rery  slightly  from  each  other— in  most  cases  not 


OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST   T,    1869.  131 

A  general  meau  of  observations  of  this  character,  made  on  seven  different  days  at  or  iiear  the 
time  at  which  totality  would  occur,  gave  for  the  sun's  actinic  force  at  that  period  0.374,  the  chem- 
ical intensity  at  noon  being  taken  as  1.000.  But  since  a  collodion  plate  is  probably  not  so  sensi- 
tive to  a  diminution  of  chemical  force  in  the  light  as  silvered  paper,  I  considered  it  safe  to  estimate 
that,  on  account  of  the  time  of  day  at  which  totality  would  occur,  the  calculated  exposure  should  be 
just  doubled.  The  difference  in  time  of  year  and  latitude  between  De  La  Hue  and  myself  on  the 
occasion  of  the  two  eclipses  being  too  inconsiderable  to  affect  the  question  of  length  of  exposure,  I 
thus  obtained  twenty-three  seconds  as  the  equivalent  with  my  telescope  of  the  one-minute  exposure 
given  by  that  astronomer.  With  this  estimate  I  had  to  allow  on  the  one  hand  for  the  fact  that  De 
La  Rue's  negatives  were  considerably  over-exposed,  and  as  an  offset  on  the  other  for  the  considera- 
tion that  I  did  not  propose  to  use  such  very  sensitive  chemicals  as  he  describes  his  to  have  been. 
Weighing  these  two  considerations  against  each  other,  I  estimated  that  about  ten  seconds  should, 
under  the  circumstances,  yield  a  negative  properly  timed  for  the  protuberances,  upon  which,  by  the 
help  of  Mr.  Le  Merle's  well-bromized  collodion,  the  corona  might  also  be  shown  to  some  extent.  I 
accordingly  determined  to  give  the  first  plate  this  exposure,  designing  this  negative  especially  for 
the  prominences,  which  would  of  course  be  seen  to  best  advantage  during  the  first  and  last  few  sec- 
onds of  duration  of  totality.  The  second  plate,  to  be  exposed  while  the  first  was  in  process  of  devel- 
opment in  the  dark-room,  I  determined  should  have  from  thirty  to  forty  seconds,  for  the  purpose  of 
representing  the  corona.  After  these  two  I  would,  of  course,  be  guided  by  word  from  the  dark- 
room. How  these  estimates  were  modified  on  the  occasion  of  the  eclipse,  on  account  of  the  bad 
weather,  will  be  detailed  further  on. 

4.  Plan  of  operation*  during  1lte  edi])ne. — After  experimenting  to  see  how  best  to  dispose  of  our 
force,  and  divide  the  labor  during  the  eclipse,  we  settled  down  to  the  following  plan,  which  was 
strictly  followed:  The  first  operator,  Mr.  Ward,  was  to  coat  the  plates  and  put  them  into  the  baths; 
the  second,  Mr.  Brennan,  to  take  them  out,  wipe  their  backs,  place  them  into  the  holders,  and  pass 
the  latter  out  to  me  by  means  of  one  of  the  dumb-waiters  in  the  wall.  My  own  duty,  as  third  ope- 
rator, was  to  take  the  plate-holder  from  the  dumb-waiter,  place  it  in  the  camera,  draw  the  slide, 
adjust  the  telescope,  (whose  position  was  invariably  disarranged  by  shifting  the  holders,)  expose  at 
a  predetermined  second  of  time  by  a  chronometer  standing  at  my  elbow  strapped  to  a  tripod  stand, 
return  the  holder  to  the  dark-room  by  the  second  dumb-waiter,  and  then  record  the  instant  of  the 
exposure  on  a  sheet  of  paper  tacked  to  a  shelf.  The  fourth  operator,  Mr.  Le  Merle,  was  to  take  the 
plate  from  the  holder  when  returned  to  tlie  dark-room,  develop,  wash,  and  drop  it  into  one  of  the 
grooves  in  the  large  fixing  trough.  There  the  plates  were  to  remain,  slowly  fixing,  until  the  eclipse 
was  over,  when  they  were  to  be  taken  out  in  the  exact  order  in  which  they  had  been  put  in,  washed, 
and  numbered  with  a  diamond ,  By  this  even  distribution  of  labor,  and  by  the  help  of  the  dumb- 
waiters and  the  large  fixing  trough,  we  found  upon  trial  that  we  could  take  negatives  at  the  rate  of 
twenty  in  fifteen  minutes.  But  desiring  that  all  the  operations  should  be  performed  with  perfect 
deliberation,  and  conceiving  that  the  number  of  negatives  that  would  be  taken  during  the  eclipse 
at  the  above  rate  was  unnecessarily  great,  I  determined  to  limit  the  exposures  to  one  each  minute, 
(except  at  the  times  of  first  and  last  contact  and  during  totality,)  so  that  all  the  operators  having 
ten  or  fifteen  seconds  to  spare  with  each  plate  could  do  their  work  coolly  and  carefully.  For  total- 
ity, the  arrangement  was  that  at  two  minutes  before  the  time  of  its  commencement  I  was  to  cease 
exposing  and  call  "Prepare  for  totality."  All  three  operators  in  the  dark-room  were  then  to  take 
out  plates  from  the  baths  and  rapidly  fill  all  four  of  the  plate-holders.  Brennan,  then  leaving  the 
dark-room,  was  to  assist  me  at  the  telescope  by  handing  me  the  holders,  taking  them  again  from 
me,  and  recording  the  times  of  exposure  as  I  called  them  out  from  the  chronometer.  This  plan  was 
on  the  supposition  that,  with  a  clear  sky  and  with  exposures  varying  from  ten  to  forty  seconds,  four 
or  five  negatives  might  be  secured  during  the  duration  of  the  total  phase.  While  developing  the 
first  totality  negative  it  was  also  Mr.  Le  Merle's  duty  to  judge,  as  soon  as  possible,  by  the  manner 
in  which  the  image  came  up  under  the  developer,  what  modification  in  the  exposure  for  the  promi- 

at  all — that  the  results  obtained  on  different  days  an'  quite  comparable  with  each  other.  lu  the  ease  of  the  observa- 
tions on  the  3d  of  August,  however,  allowance  must  be  made  for  the  fact  that  the  standard  slip  was  not  exposed  till 
after  three  o'clock  in  the  afternoon,  at  which  time,  as  the  results  of  other  days  show,  the  diminution  of  chemical  inten- 
sity of  sunlight  has  commenced.  The  two  slips  exposed  on  July  27  are  only  comparable  between  each  other  on  account 
of  the  hazy  atmosphere  of  that  day. 


132  REPORT    OF   DR.    CURTIS. 

nences  should  be  made  iu  the  succeeding  plates,  and  to  call  out  .the  same  lor  my  guidance.  During 
the  two  minutes,  also,  covering  respectively  the  times  of  the  first  and  last  contacts,  it  was  suggested 
by  Professor  Harkuess  to  take  negatives  as  fast  as  they  could  be  run  through  the  camera,  and 
accordingly  the  same  plan  as  for  totality  was  adopted  for  these  occasions,  with  the  addition  that 
Professor  Harkness,  being  then  at  leisure  from  his  own  duties,  should  assist  by  attending  to  the 
adjustment  of  the  telescope,  leaving  me  nothing  to  do  but  to  shift  the  plate-holders  in  the  camera 
and  make  the  exposures. 

V.— THE  ECLIPSE. 

For  three  weeks  before  the  7th  of  August  the  weather  had  been  magnificent,  day  following  day 
with  the  sun  unobscured  from  rising  to  setting,  and  the  atmosphere  beautifully  clear.  But  at  sun- 
set on  the  4th  the  west  was  streaked  with  ominous  "mare's  tails,''  and  for  the  following  forty-eight 
hours  the  sky  was  overcast  with  rain-clouds,  the  air  loaded  with  moisture,  and  the  wind  strong  from 
the  northeast.  The  morning  of  the  7th  dawned  upon  a  similar  day.  but  before  eight  o'clock  the  wind 
shifted  to  the  southeast  and  the  clouds  rapidly  broke  up  and  cleared  away,  leaving,  however,  to  my 
sorrow,  a  dense  ha/e  in  the  air  that  foretold  of  long  photographic  exposures  and  thin  negatives. 
Our  preparations  were  complete.  I  had  a  rope  stretched  around  the  observatory  at  a  distance  of 
a  hundred  yards,  and  by  the  kindness  of  Mayor  Hatch,  of  Des  Monies,  we  were  furnished  with  two 
special  policemen,  who  performed  most  thoroughly  their  duty  of  keeping  beyond  this  barrier  the 
crowd  that  nocked  to  the  place  in  the  afternoon.  In  the  photographic  line  one  hundred  and  fifty 
plates  had  been  cleaned  and  carefully  inspected,  so  that  all  used  might  be  faultless.  During  the 
morning  the  baths  were  freshly  filtered  and  tested  by  taking  some  stereoscopic  views;  four  gallons 
of  developer  mixed  iu  a  large  jar,  and  the  collodion  decanted  from  the  large  stock  bottles  in  which 
it  had  been  ripening  into  eleven  wide-lipped  vials  of  about  eight  ounces  capacity.  These  were  filled 
about  three-quarters  full,  and  were  to  be  nsed  in  turn  till  half  empty.  The  dark-room  and  camera- 
box  were  thoroughly  sponged  out,  the  plate-holders  tried  to  see  if  the  slides  ran  free,  and  all  the  sur- 
faces rubbed  with  paraffine.  The  paper  on  which  to  record  the  exposures  was  tacked  down  to  the 
shelf  between  the  dumb-waiters,  and  before  the  commencement  of  the  eclipse  two  lanterns  were 
lighted  and  hung  so  as  to  illuminate  this  shelf  and  my  chronometer.  Against  the  wall,  near  by, 
were  hung  memoranda  of  the  exact  time  of  commencement  and  termination  of  the  several  phases  of 
the  eclipse,  calculated  for  the  chronometer  I  was  to  use,  by  Professor  Safford,  of  the  Chicago  Obser- 
vatory, and  also  of  the  proportions  of  the  areas  of  the  different  diaphragm  apertures  to  be  nsed  over 
the  object-glass  of  the  telescope,  to  guide  me  iu  estimating  the  exposures. 

As  soon  as  the  sun  crossed  the  ridge-pole  of  the  observatory  Professor  Harkness  and  I  adjusted 
the  eye-piece  of  the  telescope  so  that  the  position  wires  should  be  approximately  at  4f>°  to  a  parallel 
of  declination,  and  clamped  it  immovably.  Then  to  determine  the1  exact  position  of  the  wires,  the 
Professor  observed  on  the  ground-glass  screen  three  transits  of  the  sun  across  each  wire.  These 
observations  were  also  repeated  immediately  after  the  eclipse  was  over.  As  soon  as  the  position 
wires  were  set  we  commenced  taking  solar  negatives,  in  order  to  test  the  amount  of  exposure  that 
the  hazy  atmosphere  would  necessitate,  and  to  be  sure  of  the  condition  of  the  chemicals.  Every- 
think  worked  perfectly  at  first,  but  about  half  an  hour  before  the  time  for  commencement  of  the 
eclipse,  to  our  dismay,  jet-black  spots,  such  as  none  of  us  had  ever  seen  before,  suddenly  appeared 
on  every  plate.  These  did  not  come  up  during  development,  but  only  after  the  water  was  turned  on 
to  icash  off  the  developer.  Suspicion  at  once  attached  to  the  well-water  with  which  the  barrel  was 
filled,  although  we  had  been  using  it  for  washing  negatives  for  two  weeks  with  perfect  success,  and 
it  had  worked  well  that  very  morning  on  some  stereoscopic  plates.  A  plate  was  accordingly  rapidly 
exposed,  developed,  and  washed  with  (Unfilled  water.  It  came  up  perfectly  clean,  thus  proving  the 
trouble  to  be  in  the  water.  Fortunately,  in  order  to  provide  against  every  contingency,  I  had  pre- 
viously had  hauled  to  the  observatory  a  large  cask  of  cistern  water;  so  we  rapidly  emptied  our 
barrel  of  the  well-water  and  filled  it  from  the  cask,  while  Mr.  Breunan  started  off  at  a  run  to  engage 
a  man  to  bring  more  water  from  the  nearest  cistern  in  the  neighborhood  during  the  progress  of  the 
eclipse,  so  that  there  might  be  no  danger  of  our  running  short.  In  the  mean  time  Mr.  Ward  was 
coating  the  batch  of  plates  for  the  first  rapid  exposures.  Taught  by  the  preliminary  practice  we 
had  just  had,  I  arranged  the  telescope  with  the  slit  in  the  instantaneous-plate  at  its  widest — half  an 


OBSERVATIONS   OF   THE   ECLIPSE    OP   AUGUST   7,    1869.  133 

inch — and  with  six  inches  aperture  to  the  object-glass.  At  9h  59"'  57N  by  my  chronometer  I  made 
the  first  exposure,  and  passed  seven  plates  through  the  camera  in  rapid  succession,  as  had  been 
arranged.  An  interval  of  about  four  minutes  then  elapsed  while  Mr.  Ward  refilled  the  baths,  after 
which  we  settled  down  to  our  steady  work  of  one  plate  a  minute.  At  the  thirty-ninth  plate,  Mr. 
Le  Merle  calling  for  more  exposure,  I  removed  the  diaphragm  cap  from  the  object-glass,  and  from 
that  time  on  worked  with  the  full  aperture,  of  the  lens.  As  the  eclipse  advanced  and  the  sun's  disk 
narrowed  to  a  crescent  the  light  became  very  gloomy,  and  the  air  growing  suddenly  damp  and 
chilly,  I  was  glad  to  don  a  coat  to  prevent  shivering.  At  the  same  time  the  image  from  the  finder 
on  the  ground-glass  became  so  faint  that  I  was  obliged  to  slip  up  the  white  card-board  screen  that 
had  been  prepared  for  use,  during  totality.  At  exactly  two  minutes  before  the  calculated  time  for 
the  commencement  of  that  phase  I  gave  the  prearranged  signal  to  the  operators  in  the  dark-room. 
The  four  plate-holders  were  then  quickly  filled,  and  Brennan  came  out  to  assist  me.  A  holder  was 
placed  in  the  camera  and  the  telescope  was  adjusted  as  well  as  possible  by  the  fine  crescent  image 
of  the  sun.  With  my  back  to  the  heavens  and  my  eye  riveted  upon  this  little  image  on  the  white 
card-board,  I  watched  it  shrink  to  a  mere  line,  and  then  suddenly  melt  away  in  all  directions  like 
an  icicle  thrown  into  boiling  water.  With  its  fading  came  a  solid,  rushing  darkness,  that  seemed 
to  grow  in  the  very  air  and  close  upon  me  from  all  sides,  producing  a  strange  sensation  as  of  positive 
eugulfment  by  something  black  and  material,  whose  embrace  was  all  the  more  thrilling  from  being- 
swift,  noiseless,  and  impalpable.  Out  went  the  last  twinkle  of  sunlight,  and  out  flashed  the  light 
in  the  lantern  swinging  by  my  chronometer,  as  suddenly  as  the  blaze  from  a  match  struck  in  the 
dark.  The  totality  had  come,  and  the  "Oh!  Oh!  Oh!"  of  the  distant  crowd  which  had  followed  the 
rapid  fading  of  the  sunlight  changed  to  one  shout  of  admiration,  and  was  then  suddenly  hushed. 
But  to  me  the  moment  was  one  of  dismay,  for,  with  the  vanishing  of  the  sun's  image  from  the  card- 
board screen,  a  most  unexpected  difficulty  presented  itself,  which  threatened  to  destroy  all  chance 
of  making  but  one  exposure  during  the  totality.  This  was  that  the  image  of  the  corona  thrown  by 
the  finder  was  so  excessively  taint  that  at  first  I  could  see  absolutely  nothing  upon  the  screen  when 
the  sun  disappeared.  But,  as  previously  mentioned,  the  telescope  required  readjusting  after  each 
change  of  plate-holders  in  the  camera,  no  matter  how  carefully  that  operation  was  performed,  and 
it  instantly  flashed  through  my  mind,  how  will  it  be  possible  to  effect  this  readjustment  after  the 
present  plate  is  removed,  if  the  image  from  the  finder  is  too  faint  to  be  seen  ?  Fearing,  then,  that 
everything  would  have  to  be  staked  upon  the  single  plate  already  in  the  instrument,  1  shrank  from 
making  the  exposure  until  I  could  be  absolutely  sure  that  in  this  case,  at  least,  the  rather  uncertain 
preliminary  adjustment  by  the  fast  dwindling  crescent  of  sunlight,  was  correct.  I  therefore  strained 
my  eyes  to  the  utmost,  and  at  last,  by  putting  my  face  close  to  the  screen,  was  able  to  make  out  a 
faint  halo  of  light,  defining  the  disk  of  the  dark  moon.  Seeing,  then,  that  the  centering  of  the 
image  was  very  nearly  exact  as  the  telescope  stood,  I  wasted  no  time  attempting  to  better  it,  but 
at  once  threw  open  the  shield  to  make  the  exposure.  This  difficulty  of  the  faintness  of  the  image 
of  the  corona  was  totally  unexpected,  and  the  more  provoking  because,  to  make  sure,  as  I  thought, 
that  I  was  secure  against  just  this  mishap,  and  that  the  plan  of  receiving  the  image  from  the  finder 
upon  white  card-board  was  safe  for  use  during  totality,  1  had  previously  carefully  tested  the  arrange- 
ment upon  the  moon,  whose  light  that  of  the  corona  was  universally  held  to  equal,  and  had  found 
that  I  could  see  the  image  of  that  luminary  upon  the  screen  with  perfect  distinctness  when  standing 
so  as  to  command  the  adjusting-screws  of  the  telescope.  Whether  it  was  that  the  real  amount  of 
light  of  the  corona  has  been  overestimated,  or  whether  its  feebleness  on  this  occasion  was  entirely 
due  to  the  prevailing  haze,  I  cannot,  of  course,  positively  say,  but  am  inclined  to  think  that  most 
of  the  trouble  was  from  the  latter  cause. 

After  starting  the  exposure  and  calling  the  time  by  the,  chronometer  for  Brennau  to  record,  I 
turned  to  gaze  at  the  heavens.  My  first  feeling,  I  confess,  was  one  of  slight  disappointment  at  the 
appearance  of  the  corona,  which  did  not  look  as  bright  or  extensive  as  I  had  been  led  to  expect  from 
the  various  drawings  of  previous  eclipses.  It  seemed  to  extend  to  a  distance  equal  only  to  one-fifth 
or  one-quarter  of  the  moon's  diameter.  But  the  magnificence  of  the  red  prominences,  and  the  dis- 
tinctness with  which  they  could  be  seen  by  the  naked  eye,  filled  me  with  astonishment,  for  I  had 
supposed  they  would  scarcely  be  visible  without  a  glass,  especially  to  slightly  near-sighted  eyes  like 
mine.  They  were,  however,  readily  to  be  seen,  and,  instead  of  being  a  "pink"  or  "rose"  color,  they 


134  REPORT    OF   DR.    CURTIS. 

looked  to  me  of  a  pure,  rick  carmine  tint,  and  .seemed  to  glow  and  sparkle  as  if  the  moon  were  a 
disk  of  jet  studded  ou  its  eastern  side  with  rubies  or  garnets  flashing  in  the  sun.  Glancing  at  the 
surrounding  sky,  I  observed  two  stars,  probably  Venus  and  Mercury,  though  I  made  no  note  of 
their  position.  The  appearance  of  the  sky  was  different  from  what  I  had  expected,  the  color  being 
rather  a  leaden  bluish-gray  than  the  deep  indigo  generally  observed  where  the  atmosphere  has  been 
clear.  Of  the  degree  of  darkness  I  can  form  no  estimate;  I  never  once  thought  of  it;  and  have 
only  a-  vague  remembrance  that  after  the  effect  of  the  first  rush  of  the  shadow  had  subsided  it  was 
not  really  dark.  Indeed,  I  was  so  intensely  absorbed  in  my  work,  and  so  dreadfully  anxious  for  the 
success  of  the  plate,  in  the  camera,  upon  which  1  then  believed  that  the  only  chance  of  securing  a 
photograph  of  the  totality  was  staked,  that  I  really  paid  no  attention  to  anything  but  the  chronom- 
eter beats,  and  my  impression  of  the  appearance  of  the  phenomena  already  described  is  only  as 
of  some  dimly-remembered  dream.  Of  the  landscape  and  horizon  I  saw  nothing,  being  shut  in  by 
the  walls  of  the  observatory. 

As  to  the  length  of  exposure  to  be  given  to  the  plate  in  the  camera,  the  unfortunate  weather 
had,  of  course,  upset  my  predetermined  estimate,  and  I  was  obliged,  during  the  progress  of  the 
eclipse,  to  make  the  following  rapid  calculation  of  the  additional  time  that  the  hazy  atmosphere 
would  necessitate.  At  the  thirty-ninth  plate,  Mr.  Le  Merle  calling  for  more  exposure,  1  was  forced 
to  work  with  the  full  aperture  of  the  object-glass;  that  is,  I  was  using  an  aperture  of  seven  and 
three-fourths  inches  in  diameter,  when  two  and  one-half  or  three  ordinarily  sufficed;  or,  in  other 
words,  taking  the  proportions  of  the  squares  of  these  diameters,  I  was  giving  at  the  time  of  the 
fortieth  negative  from  six  to  ten  times  the  usual  exposure.  At  this  rate,  then,  allowing  for  the  pro- 
gressive diminution  of  actinic  force  as  the  sun  and  moon  sank  lower  in  the  heavens,  the  totality  ex- 
posures should  be  at  least  ten  times  the  original  estimates;  or,  my  shortest  exposure  for  the  prom- 
inences should  be  a  minute  and  forty  seconds,  and  the  longer  timing  intended  especially  for  the 
"corona  would  be,  of  course,  impossible.  But,  from  the  effect  of  the  progressive  motion  of  the  moon 
in  successively  covering  up  the  eastern  and  bringing  into  view  the  western  prominences,  I  consid- 
ered one  minute  as,  imder  any  circumstances,  the  longest  available  time,  for  an  exposure.  This 
amount,  therefore,  I  determined  to  give  the  negative,  and  so  notified  Mr.  Le  Merle,  warning  him, 
however,  that  the  plate  would  probably  be  under-exposed,  and  that  he  must  do  his  best  by  a  pro- 
longed development.  As  a  matter  of  fact,  I  ran  the  exposure  six  seconds  over  the  minute. 

After  removal  of  the  first  a  second  plate-holder  was  slid  into  the  camera,  though  with  grave 
doubts  in  my  mind  if  it  could  be  used,  on  account  of  the  difficulty  of  seeing  the  image  from  the 
finder,  by  which  to  adjust  the  telescope.  Again  I  strained  my  eyes  to  the  utmost  to  catch  the  faint 
glimmer  of  light  on  the  screen.  At  first,  as  before,  the  card-board  was  an  absolute  blank,  but  gradu- 
ally, as  the  pupils  of  my  eyes  dilated,  I  could  see  a  faint  image,  and,  by  dint  of  turning  the  adjust 
ment  screws  by  guess,  and  then  stooping  over  the  screen  to  see  what  effect  was  produced,  1  managed 
at  last  to  bring  the  image  into  tolerable  centering,  when,  without  waiting  to  make  the  adjustment 
perfect,  I  whirled  open  the  shield  to  make  the  exposure.  But  thirty-seven  precious  seconds  had 
been  consumed  in  this  annoying  method  of  adjusting;  we  were  in  the  last  minute  of  totality;  and 
I  listened  in  great  anxiety  for  word  from  the  dark-room  to  regulate  the  length  of  exposure.  Fifteen 
more  seconds  passed,  when  Mr.  Le  Merle  called  out,  "Double  the  time,"  and  my  heart  sank  as  the 
inexorable  chronometer  showed  that,  instead  of  double  the  exposure,  this  plate  must  have  even  less 
than  the  first.  I  believed  that  the  totality  pictures  would  be  failures,  but,  to  secure  all  the  effect 
possible,  I  ran  the  exposure  of  the  second  plate  to  within  one  second  of  the  calculated  time  for  the 
reappearance  of  the  sun.  This  calculation,  however,  proving  not  to  be  accurate,  the  last  nine 
seconds  of  totality  were  lost,  and  I  was  putting  the  third  holder  into  the  camera  when  a  spark  of 
sunlight  reappeared.  Kapidly  shifting  the  slider  to  bring  the  instantaneous  apparatus  iuto  play 
again,  and  adjusting  as  quickly  as  possible,  I  touched  off  the  trigger  and  secured  a  negative  (No. 
64)  showing  a  fine  crescent  of  the  sun  not  over  a  thirtieth  of  an  inch  in  thickness  at  the  middle. 
And  now  I  was  cheered  by  hearing  from  the  dark-room  that  tinder  a  prolonged  development  the 
totality  pictures,  which  at  first  seemed  to  be  hopelessly  under-exposed,  had  come  up  well  and  showed 
beautiful  detail  in  the  prominences,  with  a  very  fair  indication  of  the  corona.  We  now  returned 
to  the  routine  work  of  one  plate  each  minute,  except  a  break  after  the  ninety-second  plate  of  two 
minutes,  when,  OM'ing  to  the  flexure  of  the  long  telescope-tube  as  it  swung  more  and  more  hori- 


1869.  135 

zoiital,  \ve  were  forced  to  stop  and  readjust  the  centering  of  the  finder.  Near  the  time  of  last  con- 
tact, also,  the  rate  was  changed,  and  seven  plates  were  run  through  the  camera  as  fast  as  we  could 
shift  them,  in  the  same  manner  as  at  the  commencement  of  the  eclipse.  Finally,  immediately  after 
the  last  exposure  had  been  made,  Professor  Harkness  took  another  set  of  transit  observations  on 
the  ground  glass  screen  of  the  camera,  to  determine  the  exact  position  of  the  wires  in  the  eye-piece. 

VI.— THE  PHOTOGRAPHS  AND  THEIR  TEACHINGS. 

1.  Photographs  of  the  partial  phases. — These  negatives,  one  hundred  and  thirteen  in  number, 
(counting  out  four  exposures  that  prove  to  have  been  made  immediately  before  and  after  the  times 
of  the  external  contacts  and  three  negatives  that  were  spoiled,)  were  taken  solely  for  astronomical 
purposes,  and  form  an  invaluable  series  of  accurate  observations  upon  the  eclipse.  Their  measure- 
ment and  astronomical  discussion  belong,  of  course,  to  the  United  States  Naval  Observatory,  and 
the  work,  I  understand,  will  be  immediately  taken  in  hand  by  Professor  Harkness.  The  instants  of 
exposure  of  the  negatives  were  timed — touching  the  trigger  of  the  instantaneous  apparatus  always 
at  a  predetermined  even  second — by  an  excellent  mean-time  chronometer,  Negus  1275,  which  was 
compared  daily  by  Professor  Eastman  with  the  standard  Negus  1300,  whose  error  and  rate  in  turn 
Professor  Harkness  determined  by  frequent  sextant  observations.  The  record  of  these  negatives, 
as  well  as  of  those  of  the  sun  taken  on  other  days,  is  given  in  Schedule  A. 

As  regards  the  appearance  of  the  negatives  from  a  purely  photographic  point  of  view,  I  cannot 
but  feel  some  regret  that  the  unfortunate  weather  should  have  somewhat  marred  their  beauty.  In  the 
first  place,  the  haze  required  the  whole  diameter  of  the  object-glass  of  the  telescope  to  be  used,  and 
with  this  aperture  the  photographic  definition  of  the  instrument  was  under  any  circumstances 
inferior  to  that  afforded  with  the  usual  two  or  three-inch  diaphragm  cap.  Moreover,  the  haze  inter- 
fered directly  with  the  sharpness  of  the  pictures,  the  negatives  showing  a  great  and  interesting 
difference  in  appearance,  according  as  the  haze  was  lighter  or  denser  at  the  times  of  the  various 
exposures.  And  the  suddenness  of  the  changes  in  the  density  of  the  mist  as  thus  recorded  is 
quite  remarkable,  two  consecutive  negatives,  taken  at  minute  intervals  only,  sometimes  exhibiting 
extremes  of  contrast  from  this  cause.  At  one  time,  indeed,  the  haze  was  so  strong  that  the  atmo- 
sphere, for  some  little  extent  around  the  solar  crescent,  was  sufficiently  luminous  to  imprint  itself  on 
the  negative  even  during  the  fraction  of  a  second  that  the  latter  was  exposed.  In  a  large  number 
of  the  plates  the  lower  portion  of  the  sun  is  partially  obscured,  and  the  sharpness  of  the  limb  lost 
by  the  effect  of  a  photographically  dense  belt  of  haze  that  hung  tenaciously  over  that  portion  of 
the  solar  disk.  These  negatives,  therefore,  cannot  be  read  by  the  plan  of  measuring  the  distance 
apart  of  the  cusps.  But  since  the  effect  of  lack  of  perfectly  sharp  definition  upon  the  main  por- 
tion of  the  limbs  of  the  sun  and  moon  has  been  merely  to  smooth  somewhat  their  naturally  rough 
and  uneven  outline,  the  centers  of  the  two  disks  can  be  found  with  as  great  accuracy  as  if  the  defi- 
nition were  absolutely  perfect,  and  by  following  therefore  the  method  of  reading  by  determining 
the  distance  apart  and  position  of  the  centers,  the  value  of  the  negatives  for  astronomical  purposes 
will  probably  be  found  not  to  be  in  the  least  impaired  by  the  effects  of  the  hazy  weather. 

These  partial-phase  photographs  exhibit  very  well  a  physical  phenomenon  that  has  been  often 
noticed  before,  namely,  an  apparent  increased  brightness  of  that  portion  of  the  solar  disk  imme- 
diately bordering  the  projection  of  the  dark  limb  of  the  moon.  The  cause  of  this  easily-explained 
appearance  has,  so  far  as  I  know,  been  invariably  misconceived  by  such  astronomers  as  have  dis- 
cussed the  matter,  its  occurrence  having  been  even  adduced,  most  erroneously,  as  evidence  in  favor 
of  the  existence  of  a  lunar  atmosphere.*  On  account,  therefore,  of  the  very  important  bearings 
which  this  simple  little  glow  of  light  has  been  made  to  assume,  a  thorough  understanding  of  its 
true  explanation  becomes  quite  necessary. 

The  phenomenon,  first  observed  by  Professor  Stephen  Alexander,  in  1831,  was  specially  looked 
for  and  again  found  by  him  in  his  expedition  to  Labrador  on  the  occasion  of  the  eclipse  of  1860.  In 
his  report  on  that  expeditionf  he  states  that  it  was  seen  by  himself  and  three  other  observers,  was 
plainly  depicted  on  the  photographs,  anil  also  "  is  unquestionably  pictured  in  the  copies  of  daguer- 

'"On  the  Indications  by  Phenomena  of  Atmospheres  to  the  Sun,  Moon,  and  Planets."  By  Professor  Challis. 
Monthly  Notices  of  the  Royal  Astronomical  Society,  Vol.  XXIII,  page  231. 

t  In  the  "  Report  of  the  Superintendent  of  the  United  States  Coast  Survey  for  the  year  1860." 


136  REPORT   OF   DR.    CURTIS. 

reotypcs  of  the  eclipsed  sun  taken  at  Mr.  Campbell's  observatory  in  Xew  York,  under  the  supervi- 
sion of  Mr.  Campbell  and  Professor  Looinis,  in  May,  1854."  The  Professor,  in  his  report,  offers  no 
explanation  of  the  appearance.  The  same  "bright  band"  occurred  also  in  Mr.  ])e  La  E  lie's  photo- 
graphs of  the  I860  eclipse  in  Spain,  and  was  explained  by  the  English  astronomer  royal,  Mr.  Airy, 
after  proving  that  a  lunar  atmosphere  could  not  produce  the  effect  in  question,  as  being  purely 
a  subjective  phenomenon,  due  to  the  effect  of  contrast.*  This  suggestion  Mr.  De  La  Eue  submitted 
to  experiment  t  by  cutting  out  half  the  solar  crescent  in  one  of  his  prints  and  slipping  under  the 
flap  thus  raised  a  white  background  to  take  the  place  of  the  previous  black  one.  Immediately,  he 
states,  the  bright  baud  disappeared.  Again,  upon  pasting  a  black  disk  partially  over  the  sun's 
image  in  an  ordinary  photograph  of  that  body,  he  asserts  that  the  bright  band  instantly  sprang 
up  along  the  line  of  the  artificial  moon.  He  therefore  holds  with  Mr.  Airy  that  the  phenomenon  is 
purely  an  optical  illusion. 

Now  it  is  rather  singular,  to  say  the  least,  that  this  appearance,  if  at  all  as  well  marked  in  the 
1860  photographs  as  in  those  obtained  during  the  eclipse  of  last  August,  should  have  been  so  sum- 
marily dismissed  from  existence  and  upon  the  strength  of  such  loose  tests  as  those  applied  by  Mr. 
De  La  Eue.f  Convinced  by  the  aspect  of  my  photographs  that  the  bright  band  was  not  an  optical 
illusion,  I  re-read  De  La  Rue's  account  of  his  experiments  in  the  matter,  when  it  became  evident 
at  once  that  these  were  not  conducted  with  sufficient  precision  to  be  decisive.  Thus  considering 
the  effect  to  be  wholly  one  of  contrast,  De  La  Euc  substituted  a  background  of  pure  white  in  place  of 
one  of  pure  black,  and  found  that  the  brightening  disappeared.  But  here  is  an  important  source  of 
error  in  this  method  of  testing  the  matter;  by  using  a  pure  white  background  a  contrast  the  other 
way  is  established,  for  the  white  paper  is  now  a  bright  surface  and  the  gray  disk  of  the  solar  image 
a  comparatively  dark  one,  so  that  by  the  amount  of  reversed  contrast,  as  it  might  be  termed,  the 
judgment  is  blinded  as  to  whether  the  original  bright  bordering  has  totally  disappeared  or  merely 
been  so  dimmed  in  effect  by  the  superior  brightness  of  the  brilliant  white  background  as  to  be  no 
longer  appreciable  by  the  eye.  To  make  the  experiment  fair  a  background  should  be  used  of  the  same 
tint  as  the  surface  upon  which  the  brightening  occurs,  when,  if  the  latter  is  wholly  subjective,  the 
tint  should  be  uniform  across  the  cut  edge.  Such  a  background  can  be  best  obtained  by  cutting  off  a 
piece,  in  the  very  print  to  be  tested,  from  the  opposite  non-eclipsed  side  of  the  sun  itself  and  slipping 
it  under  the  eclipsed  edge,  previously,  of  course,  cut  out  from  the  original  black  background,  so  as  to 
exactly  complete  and  fill  up  the  gap  in  the  solar  disk  originally  occupied  by  the  dark  moon.  With 
the  experiment  performed  in  this  way  it  will  be  found  that  the  bright  band  does  not  disappear,  but 
looks,  if  anything,  more  brilliant  than  before,  since  now  the  eye  appreciates  that  there  can  be  no 
deception  and  is  able  to  judge  absolutely  of  the  true  degree  of  brightness  of  the  little  ribbon  of 
light.  In  a  similar  manner  De  La  Rue's  second  experiment  is  also  wanting  in  thoroughness.  To 
show,  as  he  thought,  that  the  effect  could  be  produced  at  will  by  contrasting  a  bright  and  dark- 
surface  together,  he  pasted  a  black  disk  so  as  to  partially  cover  the  solar  image  in  an  ordinary  pho- 
tograph of  the  sun  when  not  eclipsed,  and  states  that  the  print  then  "  showed  the  brightening 
very  distinctly."  But  this  experiment  totally  fails  to  show  that  the  apparent  brightening  thus  pro- 
duced is  as  brilliant  as  that  seen  in  a  genuine  eclipse  picture,  and  therefore  does  not  prove  that  the 
latter  phenomenon  is  wholly  of  the  same  nature  as  the  former.  To  make  this  experiment  also 
accurate  it  should  be  performed  by  pasting  the  black-paper  disk  on  the  image  of  the  sun  in  the 
eclipse  picture  itself,  taking  care  to  cover  the  same  extent  of  the  solar  disk  on  the  one  side  as  that 
actually  eclipsed  oh  the  other.  If  this  be  done  it  will  be  found  that  the  appearance  of  the  faint 
brightening,  produced  by  contrast  along  the  line  of  the  black  disk,  (visible  to  some  persons,  but 
which  I  confess  I  have  never  been  able  to  see  at  all  myself,)  is  altogether  inferior  in  brilliancy  and 
extent  to  that  bordering  the  line  produced  by  the  genuine  eclipse. 

This  phenomenon,  then,  so  frequently  seen  and  photographed  during  a  solar  eclipse,  is, 
beyond  all  question,  real.  To  account  for  its  appearance,  my  first  step  was  to  ascertain  if  it  was 

*  Monthly  Notices  of  the  Royal  Astronomical  Society.  Vol.  XXIV,  pp.  13  and  188. 

t  Philosophical  Transactions,  1862,  page  368. 

t  At  the  time  of  writing  I  had  not  seen  Professor  Challis's  subsequent  papers,  (Monthly  Notices  MI' tin-  l.'nval  Astro  - 
nomical  Society,  Vol.  XXIV,  page  49,  and  Vol.  XXV,  page  18,)  in  which  he  also  calls  in  question  Messrs.  De  La  Rue  and 
Airy's  assertion  that  the  phenomenon  is  purely  subjective,  though  finally  assenting  to  Airy's  conclusion  llmt  the  exist- 
ence of  a  lunar  atmosphere  would  not  account  for  the  appearance. 


OBSERVATIONS    OF   THE   ECLIPSE    OF    AUGUST    7,    1869.  137 

peculiar  to  an  eclipse,  or  would  occur,  as  I  rather  anticipated,  whenever  the  same  optical  conditions 
were  reproduced.  To  answer  this  question,  experiments  were  made  with  a  miniature  artificial 
eclipse,  which  I  prepared  in  my  optical  room  at  the  Army  Medical  Museum  after  my  return  from 
the  West,  in  the  following  way :  For  the  sun  I  used  the  disk  of  ground  glass  that  serves  as  the  source 
of  illumination  for  photographing  certain  characters  of  microscopic  objects.  This  disk,  set  in  a  cir- 
cular brass  mounting',  is  fixed  at  the  end  of  a  short  tube  projecting  horizontally  into  the  room  from 
the  window  shutter,  and  is  illuminated  evenly  and  steadily  by  a  beam  of  sunlight  reflected  from  the 
mirror  of  a  heliostat  outside  the  window.  Exactly  in  line  with  the  axis  of  the  tube,  and  therefore 
with  the  direction  of  the  light,  a  camera  was  mounted,  armed  with  a  Dallmeyer  triplet  lens.  Rep- 
resenting the  moon  by  a  disk  of  black  paper,  my  first  experiment  was  to  paste  this  disk  directly 
upon  the  ground  glass,  adjust  the  focus  for  the  two  together,  and  then  take  an  instantaneous  picture. 
As  was  expected,  a  print  from  this  negative  showed  not  the  slightest  trace  of  a  bright  border  to 
the  line  of  the  dark  disk.  I  next  placed  the  artificial  moon  three  -inch en  or  so  in  front  of  the  sunlit 
ground  glass,  so  that  its  image  in  the  camera  should  appear  to  eclipse  about  one-third  of  the  ground- 
glass  disk,  then  changed  the  focus  to  correspond  with  the  altered  distance  of  the  "  moon,"  so  as  to 
preserve  the  image  of  its  edge  sharp,  and  again  exposed  instantaneously.  The  photograph  thus 
obtained  bore  an  astonishingly  close  resemblance  to  a  picture  of  the  sun  partially  eclipsed ;  so  close 
indeed,  as,  at  the  first  glance,  to  completely  deceive  Professor  Ilarkness,  who  happened  in  shortly 
after  the  negative  was  taken,  and  to  whom  I  merely  showed  it  without  comment.  The  ground 
glass  being,  of  course,  somewhat  out  of  focus,  appears  most  strongly  illuminated  in  the  center,  with 
a  gradual  and  uniform  diminution  of  brightness  toward  the  edges,  precisely  like  the  appearance 
of  the  sun  itself,  while  the  grain  of  the  glass  represents  very  well  the  mottling  of  the  solar  surface. 
But  most  striking  of  all  is  the  riritl  bonier  of  increased  brightness  adjoining  the  edge  of  the  imitation 
moon.  This  appearance,  identical  in  all  respects  with  that  shown  by  the  eclipse  pictures,  is  even 
more  unmistakably  marked.  But  to  submit  the  question  of  its  actual  existence  to  a  rigid  test,  1 
cut  out  a  second  disk  of  blackened  photographic  paper  and  pasted  it  on  one  of  the  prints  over  the 
opposite  side  of  the  artificial  sun  from  that  eclipsed,  being  careful  that  it  should  cover  the  same 
extent  of  the  solar  disk  as  the  amount  eclipsed  by  the  mock  moon.  The  print  was  then  strongly 
rolled  and  shown  independently  to  four  different  persons,  who  were  totally  ignorant  of  what  it  was 
intended  to  represent,  or  of  what  they  were  expected  to  see.  Each  was  merely  asked  if  he  observed 
any  difference,  without  a  hint  as  to  the  /.•/»<?  of  difference,  between  the  two  concave  edges  presented 
by  the  picture  of  the  "  sun."  Three  replied  instantly  and  unhesitatingly,  yes ;  that  one  border  was 
brighter  than  the  other,  all  designating  for  the  edge  possessing  this  bright  border  that  of  the  arti- 
ficial moon.  The  fourth  answered  equally  promptly  that  one  looked  "  sharper"  than  the  other;  and 
being  asked  to  define  what  he  meant  by  "  sharper,"  replied  that  one  edge  appeared  to  standout 
more  vividly  sharp  and  clear  cut,  because  the  gray  background  iras  lighter  immediately  along  its  bor 
tier  than  on  the  opposite  x'«lc.  lie  also,  of  course,  pointed  out  the  "eclipse"  edge  as  that  adjoining 
which  the  brightening  occurred.  To  make  sure  that  the  appearance  was  not  a  chance  eftect  on  thai 
particular  negative,  owing  to  some  unnoticed  error  in  the,  method  of  conducting  the  experiment,  I 
repeated  the  hitter  on  another  day,  taking  a  second  negative  with  a  flat  disk  for  the  moon,  and  a 
third  with  the  bowl  of  a  hemispherical  porcelain  capsule  substituted  for  the  disk.  The  effect  was 
I  lie  same — an  increased  brightness  along  the  line  of  the  imitation  eclipse.  A  final  test  was  made 
with  one  of  the  negatives  itself,  placing  beneath  it  a  piece  of  paper  on  which  was  a  line  of  printed 
dots.  Holding  the  negative,  then,  to  the  light  the  dots  could  be  plainly  seen  even  through  the  cen- 
ter of  the  image  of  the  ground  glass,  but  close  to  the  concave  edge  of  the  artificial  moon  they  dis- 
appeared, nor  could  any  amount  of  straining  of  the  eyes  make  them  visible;  showing  that  for  a 
narrow  space  bordering  this  edge  the  silver  deposit  in  the  negative  was  actually  denser  than  on  the 
rest  of  the  image  of  the  mock  sun. 

These  artificial  eclipse  photographs,  thus  proving  conclusively  that  the  phenomenon  in  ques 
tion  could  be  made  manifest  at  will  by  photographing  any  opaque  body  seen  projected  against  a 
distant  luminous  surface,  suggested  at  once  that  the  appearance  ought  to  be  one  of  common  occur- 
rence in  photographs,  since,  of  course,  these  optical  conditions  are  constantly  present.  Remember- 
ing, then,  that  1  had  indeed  often  seen  a  faint  appearance  of  some  such  brightening  along  the  edge 
18* 


138  REPORT    OF   DR.    CURTIS. 

of  opaque  bodies  in  my  photographs  of  microscopic  objects  taken  through  the,  microscope  by  trans- 
mitted light,  where,  of  course,  the  required  conditions  were  present,  I  turned  first  to  my  volumes  of 
these  photographs  and  found,  as  expected,  constant  indications  of  this  increased  brilliancy  of  the 
field  of  view  as  the  edges  of  opaque  objects  were  approached.  But  the  appearance  was  always 
faint,  since  in  the  prints  the  field  of  view  itself  was  generally  but  faintly  tinted.  To  make  certain, 
therefore,  of  the  actual  presence  of  the  phenomenon,!  selected  a  negative  of  unusual  intensity,  which 
1  judged  should,  on  that  account,  show  the  brightening  very  strongly,  and  caused  to  be  taken  from 
it  a  very  deep  print,  sodeep  that  in  thefinished  picture  the  main  portion  of  the  Held  should  be  of  a  pretty 
dark  shade.  And  the  result  fairly  astonished  me  in  the  brilliancy  and  extent  of  the  glow  of  light 
represented  as  bordering  all  the  irregular  outlines  of  the  opaque  object.  Upon  the  strength  of  this 
experiment  I  next  selected,  quite  at  random,  two  ordinary  stereoscopic  negatives,  the  subject  being 
our  temporary  observatory  at  lies  Moiues  as  seen  relieved  against  the  bright  sky,  and  had  similar 
deep  prints  taken  from  them  also.  As  confidently  expected,  the  result  was  the  same ;  the  hidden 
shading  in  the  impression  of  the  sky  upon  the  negative  was.  liy  the  dec]*  printing,  forced  to  show 
itself,  and  the  building  in  the  center  of  the  pictures  appeared  bordered  by  the  same  glow  of  light 
manifest  in  the  photomicrographs  and  the  eclipse  photographs.  And  knowing  how  to  appreciate 
the  faint  manifestation  of  this  interesting  phenomenon  afforded  by  photographic  prints  of  the  ordi- 
nary intensity,  I  constantly  find  indications  of  its  presence  in  photographs  of  every  description 
where  a  dark  body  is  shown  against  a  distant  luminous  background. 

The  phenomenon,  then,  so  far  as  I  know,  unsuspectingly  supposed,  by  those  astronomers  who 
have  allowed  it  an  actual  existence  at  all,  to  be  peculiar  to  a  solar  eclipse,  is  thus  shown,  on  the  con- 
trary, to  be  of  invariable  occurrence  where  the  same  optical  conditions  obtain,  and  to  be  constantly 
recording  itself  upon  photographic  negatives  of  ordinary  terrestrial  objects.  That  it  is  not  as  con- 
stantly noticed  is  not  surprising,  when  it  is  remembered  that  the  eye  alone  can  rarely  sec  the  phe- 
nomenon, since  the  actual  increase  in  brilliancy  of  the  luminous  background  is  too  slight  to  lie 
appreciated  by  vision  in  the  presence  of  the  positive  brightness  of  the  surface  upon  which  such 
increase  occurs.  The  occurrence  of  the  brightening  in  photographs,  also,  though  1  tind  it  has  been 
frequently  noticed  by  photographers  beside  myself,  yet  does  not  arrest  serious  attention,  both 
because,  as  ordinarily  printed,  the  luminous  background  upon  which  the  brightening  occurs  appears 
itself  almost  colorless,  and  because,  as  thus  shown,  the  increase  of  brilliancy  is  generally  more 
gradual  and  diffused  than  in  the  case  of  an  eclipse,  where  there  appears  .almost  a  well  -defined  "  baud" 
of  bright  light  immediately  bordering  the  limb  of  the  moon.  The  phenomenon,  in  its  terrestrial 
manifestations,  therefore,  can  only  be  shown  by  means  of  a  very  delicate  photometer,  or  by  the  sim- 
pler method  adopted  above  of  taking  very  deep  photographic  prints  from  rather  under-exposed  and 
strongly  intensified  negatives,  which,  by  greatly  exaggerating  all  contrasts  of  light  and  shade  in 
the  original  object,  will  make  plainly  visible  a  slight  increase  of  luminosity  in  the  background  which 
might  otherwise  escape  detection. 

The  phenomenon  being  thus  found  to  be  one  of  general  occurrence,  requiring  as  conditions  only 
the  projection  of  an  opaque  body  against  a  distant  luminous  background,  it  was  evident  to  me  that 
the  explanation  must  be  sought  in  the  general  laws  of  optics,  and  diffract  ion  at  once  suggested 
itself  as  the  only  possible  cause  of  the  appearance.  Upon  analyzing,  then,  what  would  be  the  effect 
produced  by  diffraction  where,  instead  of  a  single  spherical  wave  of  light  from  a  radiant  point  fall- 
ing upon  the  diffracting  body,  an  infinite  number  of  such  waves  from  an  extended  radiant  xvrface 
were  suffered  to  impinge  upon  it,  it  became  at  once  manifest  that  not  only  miyltt  the  phenomenon 
in  question  be  explained  as  an  effect  of  diffraction,  but  that  under  the  conditions  named  just  such 
an  appearance  must  occur  as  an  inevitable  consequence  of  optical  laws.  If  we  place  in  the  path  of 
a  cone  of  diverging  rays  of  monochromatic  light,  emanating  practically  from  a  single  point,  a  solid 
obstruction  and  receive  its  shadow  upon  a  screen,  we  have  the  well-known  effect  of  diffraction — 
the  line  of  shadow  is  bordered  by  a  stripe  of  increased  brightness,  that  followed  by  a  dark  stripe. 
and  that  succeeded  by  another  bright  one,  and  so  on,  the  stripes  gradually  fading  in  intensity.  l!ut 
this  point  must  be  remembered :  if  we  take  as  a  mean  the  degree  of  brightness  produced  on  the 
screen  by  the  unobstructed  ray,  it  is  a  consequence  of  optical  laws  that  when,  by  the  interposition 
of  an  obstruction,  these  alternate  bright  and  dark  stripes  are  produced,  the  positive  elfect  of 


181)9.  139 

increase  of  brightness  above  the  mean  in  the  bright  stripe  is  always  greater  than  the  negative 
effect  of  diminution  of  brightness  in  the  succeeding  dark  one.  That  is,  the  sum  of  the  gain  of 
light  in  all  the  bright  stripes  produced  by  diffraction  is  greater  than  the  sum  of  the  loss  of  light  in 
the  dark  ones;  so  (hat  could  \ve  blend  the  bright  and  dark  stripes  together,  we  should  have,  as  the 
resultant  of  the  dillVaction  effect,  a  general  increase  of  brilliancy  upon  the  screen  bordering  the 
shadow  of  the  diffract  ing  body,  and  diminishing  in  intensity  in  the  direction  outwards  from  the 
line  of  the  shadow.  Now  this  blending  of  the  stripes  is  exactly  what  must  occur  when,  instead  of 
receiving  light  from  a  radiant  point  emitting  a  single  diverging  cone  of  rays,  the  illumination  is 
obtained  from  a  radiant  mirfdrc,  emitting  of  course  an  infinite  number  of  such  diverging  pencils 
from  points  differently  situated.  Each  of  these  pencils  will  produce  its  own  system  of  stripes  by 
impinging  upon  the  obstruction  in  its  path,  and  each  of  these  systems  will  have  a  different  locus 
according  to  the  position  of  the  individual  radiant  point  to  which  each  owes  its  origin.  And  there- 
fore, since  I  lie  radiant  points  of  the  illuminating  surface  are  infinitely  close,  the  systems  of  stripes 
must  be  indistiiiguishably  blended,  and  must,  in  accordance  with  the  above  mentioned  law  of  dif- 
fraction, produce  as  a  resultant  the,  effect  of  a  general  accession  of  light  upon  the  screen.  But  now, 
since  the  light  comes  from  an  extended  surface,  the  diffracting  body  has  no  sharp  line  of  shadow, 
and  the  accession  of  light,  produced  by  the  diffraction,  being  distributed  over  the  whole  extent  of 
the  penumbra,  cannot  be  demonstrated  by  the  method  of  receiving  the  rays  of  light  npou  an 
extended  screen.  But  if  a  lens  be  employed  and  a  sharp  image  of  the  diffracting  body  formed  in 
a  camera,  it  seemed  to  me  that  the  action  of  the  lens  in  referring  each  individual  ray  from  the  radi- 
ant surface  to  the  same  position  in  the  image  as  the  position  of  the  original  point  of  emission  in 
the  surface  itself,  should  confine  the  uppnrent  diffraction  effect  upon  the  image  to  a  comparatively 
narrow  strip  of  the  radiant  surface  adjoining  the  edge  of  the  diffracting  body,  and  thus  cause  to 
appear  on  the  screen  of  the  camera  just  such  an  apparent  smooth  increase  of  brilliancy  to  the  lumin- 
ous background  immediately  adjoining  the  line  of  projection  of  the  opaque  body  as  lias  been  shown 
to  occur  in  photographs  both  of  celestial  and  terrestial  objects  taken  under  the  above  conditions. 

Desirous,  however,  that  these  general  ideas  should  be  critically  analyzed  by  competent  author- 
ity, I  placed  a  set  of  the  various  photographs  showing  the  phenomenon  in  question,  together  with 
the  above  hypothetical  explanation  of  its  occurrence,  into  the  hands  of  Dr.  F.  A.  P.  Barnard,  Pres- 
ident of  Columbia  College,  Xew  York.  That  eminent  physicist,  admitting  at  once  the  objective 
reality  of  the  phenomenon  as  shown  by  the  photographs,  as  indeed  it  is  impossible  not  to  do,  was 
disposed  to  regard  my  explanation  as  the  only  possible  one,  and  kindly  interesting  himself  in  the 
matter,  undertook  to  study  the  subject  critically,  especially  with  reference  to  what  would  be  tne 
manifestation  of  diffraction  phenomena  in  case  an  image  of  the  obstructing  body  were  formed  in  a 
camera  by  a  lens.  The  results  of  his  analysis,  fully  confirming  the  hypothesis  advanced  as  the 
true  explanation  of  the  phenomenon  of  the  "brightening,"  Dr.  Barnard  has  communicated  to  me 
in  the  following  letter,  which  I  am  happy  to  have  his  permission  to  quote  here  in  full: 

"COLUMBIA  COLLEGE,  NEW  YOHK, 

"  President's  Room,  November  2,  1869. 

"My  I>KAI;  Sn;:  Pressing  occupations,  since  I  had  the  pleasure  of  seeing  you  here,  must  be 
my  apology  for  not  having  more,  promptly  attended  to  the  matter  on  which  you  desired  my  opinion. 
I  feel  quite  satisfied  that  you  have  hit  upon  the  correct  explanation  of  the  phenomenon  to  which 
you  drew  my  attention,  vi/:  the  reinforcement  in  a  photographic  picture  of  the  lights  along  the 
margins  of  opaque  objects  relieved  against  a  uniformly  illuminated  background.  This  effect  I 
think  to  be  evidently  due  to  the  same  causes  which,  under  circumstances  easily  realized,  produce 
what  are  called  diffraction  fringes.  To  illustrate  this  take  the  following  figure,  in  which  SS'  repre- 
sents the  visible  disk  of  the  sun,  M.M'  that  of  the  moon,  and  XY  an  indefinite  plane. 


140 


REPORT    OF    DR.    CURTIS. 


n  QP 


(L3. 


"Drawing  S  M  E,  S'  M  13,  the  limit  of  the  dark  shadow  will  be  M  E,  and  that  of  the  penumbra 
M  D.  To  any  observer  situated  between  D  and  E  the  sun  will  be  par- 
tially obscured.  Let  Abe  the  obser\er's  place,  join  A  M  and  produce' 
it  to  P.  Since  every  point  of  the  sun's  luminous  surface  may  be  taken 
as  the  origin  of  a  spherical  wave,  and  the  actual  luminous  effect  which 
reaches  any  point  as  A  is  the  resultant  of  all  these  waves,  we  may  first 
suppose  no  other  luminous  origin  but  1'  to  exist.  Then,  as  is  well 
known,  there  will  be  formed  on  the  plane  X  V,  and  near  to  A,  a  series 
of  fringes  alternately  bright  and  dark,  as  B,  B',  B",  &c.,  (these  letter* 
being  supposed  to  occupy  the  places  of  the  bright  fringes.)  At  A  itself 
the  illumination  will  be  reduced  to  one  half  that  which  the  unobstructed 
wave  would  have  produced. 

"From  A  set  off  A  C  equal  to  A  B,  join  ('  31  and  produce  it  to  Q. 
If  Q  be  taken  as  the  origin  of  a  second  spherical  wave,  it  will  produce 
a  series  of  fringes,  of  which  the  first  bright  one  will  fall  on  A.    Further 
Yon,  as  at  E,  may  be  taken  the  origin  of  a  third  wave,  of  which  the  first 
~dark  fringe  will  fall  on  A:  then  another  of  which  the  second  bright  one 


D      u      BBBAC  JE  ~ 

may  fall  on  A,  and  so  on. 

"If  we  take  unity  to  represent  the  total  illumination  produced  at  A  by  an  unobstructed  wave, 
then  the  resultant  effect  of  all  the  component  impulses  above  supposed  to  affect  that  point  will  be 
positive;  that  is,  will  exceed  the  effect  which  the  same  number  of  independent  waves  reaching  A 
without  interference  could  produce.  To  show  this,  let  m,  m',  m",  &c.,  express  the  values  of  the 
abnormal  excesses  of  light  in  the  successive  bright  fringes,  and  •«,  n',  n",  &<•.,  the  quantities  of  light 
extinguished  in  each  of  the  dark  fringes,  n  itself  being  the  amount,  suppressed  at  A  of  the  light  of 
the  wave  P,  which,  as  we  have  seen,  is  one-half.  Now,  the  values  of  m,  m',  &c.,  are  all  greater 
than  one-half,  and  those  of  n,  n',  &c.,  are  all  less  than  one-half,  except  that  of  n  itself.  Hence  the 
total  illumination  I  at  A  will  be  expressed  by  the  equation 

1=1-1-  (m  —  n)  +  (m'—n1)  +  (m"—n")  +  (m"'—n'")  .... 

in  which  all  the  terms  inclosed  by  parentheses  are  positive.  As  the  fringes  diminish  toward  B  in 
intensity,  it  is  obvious  that  the  illumination  of  the  surface  XY  will  similarly  diminish  in  brightness 
in  the  same  direction.  And  because  the  points  taken  in  the  sun's  disk  in  the  direction  PR  may  be 
innumerable  and  indefinitely  near  together,  the  decrease  of  brightness  will  be  uniform,  and  the 
fringes  as  such  will  disappear.  The  curve  ab  may  represent  this  decrease.  In  looking  upon  any 
such  extended  surface  exposed  to  the  sun's  light  we  shall,  however,  perceive  no  such  inequality, 
because  the  great  flood  of  light  from  the  portions  ot  the  disk  too  remote  from  P  to  be  affected  by 
diffraction,  as  for  instance  V,  drowns  out  the  comparatively  feeble  effect  produced  by  the  small 
number  of  rays  which  graze  the  moon's  limb.  But  if  a  very  small  perforation  be  made  in  the  plane 
XY,  supposed  opaque,  and  the  rays  passing  through  be  allowed  to  form  an  inverted  image  of  the 
sun  and  moon  upon  a  screen  behind  XY,  then  each  portion  of  the  disk  will  contribute  to  make  up 
only  its  own  part  of  the  picture,  and  the  differences  of  illuminating  power  in  the  several  points  will 
become  sensible.  This  is  what  the  camera  obscura  does;  for  though  the  objective  lens  is  not  a  point, 
yet  its  effect  is  to  confine  all  the  rays  which  proceed  from  any  point  of  the  object  to  t  he  same  point 
of  the  image;  and  hence  it  will  increase,  by  its  whole  optical  power,  the  actual  inequality  of  bright- 
ness produced  by  diffraction. 

"That  it  may  appear  how  the  unequal  illumination  ab  on  the  plane  XV  is  transferred,  in  the 
image,  to  the  margin  of  the  moon,  join  Q  A,  Q  being  the  center  of  the  wave  which  throws  its  first 
bright  fringe  on  A.  To  an  eye  at  A,  this  fringe  will  appear  to  be  at  F.  In  a  similar  manner  other 
fringes  would  be  formed  at  F'  F",  &c.,  by  other  waves.  And  the  same  causes  which  obliterate  the 
boundaries  of  the  fringes  B,  B',  B",  will  also  cause  those  of  F,  F',  F",  to  disappear. 

"The  fact  that  the  excess  of  brightness  between  A  and  I."  is  not  perceptible  on  the  indefinite 
surface  XY,  is  not  owing  simply  to  the  cause  above  assigned  for  it,  viz:  the  great  light  from  the 
large  portion  of  the  sun's  disk  which  is  uncovered;  but,  further  to  the  fact  that  the  point  A  being 
arbitrarily  taken,  a  similar  effect  might  be  argued  at  every  other  point  within  the  penumbra  between 


OBSERVATIONS    OF   THE   ECLIPSE    OF   AUGUST   7,    1869.  141 

D  and  E,  as  is  illustrated  for  the  point  I",  by  the  curve  u!  //.  Such  au  effect  would,  therefore,  be 
practically  uniform  throughout  I>K,  mid  would  not  interfere  with  the  gradually  decreasing  bright- 
ness along  XY  between  D  and  E,  due  to  the  increasing  obscuration  of  the  sun  in  the  direction  Y. 

"But  when  we  suppose  the  sun's  light  to  be  transmitted  through  the  minute  aperture  A  or 
through  a  lens,  the  excess  of  illumination  produced  by  diffraction  is  confined  to  the  rays  which 
come  from  the  points  of  the  sun's  disk  directly  iu  line  with  the  moon's  limb,  and  hence  their  superi- 
ority of  illuminating  effect  becomes  manifest. 

"Your  suggestion  that  the  diffraction  of  the  sun's  light  ought  to  produce  sensible,  fringes  in 
the  few  moments  just  preceding  total  obscuration  by  the  moon  is  just;  and  your  question  as  to 
whether  these  may  not  be  large  enough  to  admit  of  being  directly  observed  is  one  which  may  lie 
answered  by  computing  the  distances  at  which  the  successive  bright  fringes  ought  to  be  formed 
from  the  margin  of  the  shadow.  This  may  be  done  by  means  of  the  formula 


in  which  r  is  the  distance  from  the  source  of  light  to  the  diffracting  body;  n  the  distance  from  this 
body  to  the  screen  on  which  the  fringes  are  formed  ;  A  the  mean  length  of  the  luminous  undulations, 
and  •?  the  distance  sought.  This  formula  gives  the  distance  of  the  first  bright  fringe.  Those  of 
the  succeeding  fringes  will  be  obtained  by  multiplying  the  result  by  V3,  V»,  -/7,  &c. 

"Putting  r  +  s  (the  sun's  distance  from  the  earth)  at  92,500,000  miles;  s  (the  moon's  mean 
distance  from  the  earth)  at  240,000  miles,  and  /  =  ;r(TJU5  of  au  inch,  we  shall  have,  for  the  distances 
from  the  margin  of  the  shadow  of  the  first  four  fringes,  Ki  feet,  SO  feet,  103  feet,  and  122  feet 
respectively.  Though  these  alternations  of  light  and  shade  will  travel  with  great  velocity,  yet  to  an 
observer  situated  above  the  earth's  surface  at  a  moderate  distance,  it  would  seem  that  they  might 
be  perceptible. 

"  In  the  experiment  on  an  artificial  eclipse  described  by  you  .is  conducted  in  your  chamber,  the 
fringes  must  be  much  smaller.  Taking  conjecturally  »•=!  foot  and  s=10  feet,  the  value  of  3  becomes 
one-sixth  of  an  inch;  and  the  series  of  fringes  will  occupy  the  points  distant  0.10  inch,  0.28  inch, 
0.36  inch,  and  0.43  inch  from  the  border  of  the  image  of  the  eclipsing  body. 

"Please  pardon  my  delay  in  attending  to  your  questions,  and  believe  me  to  be, 

"Very  sincerely,  yours, 

"F.  A.  P.  BAKNARD. 

"Dr.  EDWARD  CURTIS, 

"Brevet  Major  United  Matrx  Army." 

The  above  clear  exposition  of  the  general  fact  that  an  appearance  similar  to  the  solar-eclipse 
phenomenon  under  discussion  must  theoretically  occur  wherever  an  image  of  an  opaque  body, 
viewed  against.a  distant  evenly  illuminated  background,  is  formed  by  a  lens,  will,  it  is  believed, 
when  taken  in  conjunction  with  the  experimental  proof  shown  to  be  afforded  by  photographs  of  all 
descriptions,  completely  set  at  rest  the  question  of  the  cause  of  the  "bright  band"  seen  to  border 
the  eclipsing  limb  of  the  moon  during  the  transit  of  the  latter  over  the  solar  disk.  And  with  the 
explanation  of  the  phenomenon  as  simple  diffraction  light,  the  last  prop  that  could  even  be  sup- 
posed to  support  the  theory  of  the  existence  of  an  appreciable  atmosphere  to  the  moon  falls  to  the 
ground.* 


"The  question  discussed  by  Dr.  Barnard  as  to  the  size  and  consequent  visibility  of  the  distinct  fringes  that  must 
theoretically  border  the  shadow  of  the  moon  occurred  to  me  from  noticing  that  Professor  Alexander,  in  his  f/ahrador 
expedition  to  observe  the  eclipse  of  July,  1860,  directed  the  seamen  on  his  vessel  to  watch  for  the  possible  appearance 
of  sueli  fringes,  and  that  the  men  reported  that  they  did  indeed  sec  sonic  •'  Hying  shadows"  and  a  "  slight  quivering  of 
the  last  beams  of  the  sun."  (Report  of  the  Superintendent  of  the  United  States  Coast  Survey  for  1860,  pp.  SMr>  and  '-'(iT. ) 
Dr.  Barnard  shows  that  the  diffract ion  Cringes  in  question  will  lie  litnir  enough  to  be  observed,  but  there  must  still 
remain  as  dilh'eulties  in  the  way  of  the  observation  the  tremendous  velocity  with  which  the  moon's  .shadow  travels  over 
the  earth  and  a  certain  amount  of  confusion  in  the  fringes  themselves,  since  a  slight  overlapping  of  independent  sys- 
tems of  fringes  must  still  persist.  The  difficulty  of  the  swiftness  of  the  llight  of  the  moon's  shadow  might,  to  a  certain 
extent,  be  avoided  by  observing  from  a  point  upon  the  exact  nxtryin  of  the  belt  of  totality,  instead  of  upon  its  central 
line,  since  at  such  a  station  the  fringes  will  rush  past  the  observer  in  the  general  direction  of  their  length  instead  of 
their  breadth,  and  will  thus  be  more  readily  detected. 


142  REPORT   OF   DR.    CURTIS. 

-'.  Photographs  of  the  totality. — It  is  a  matter  of  very  great  s;ilisl';i<-tii>ii  tliiit,  despite  all  the 
difficulties  experienced  on  account  of  the  Lazy  weather,  two  such  exquisite  negatives  of  the  total 
pliase  of  tLe  eclipse  were  secured — negatives  that  are  of  value  not  only  as  affording  pictures  per- 
fect in  every  detail  of  some  unusually  remarkable  groups  of  solar  protuberances,  but  also,  it  is 
believed,  as  marking  an  era  in  eclipse  photography,  proving,  as  they  do,  that  by  a  proper  selection 
of  chemicals  and  with  a  siitliciently  short  exposure  to  the  plates,  the  photographic  art  is  capable  of 
yielding  pictures  of  the  red  prominences  of  a  beauty  and  delicacy  of  detail  never  approached  before. 
These  negatives  show  that  even  the  most  massive  and  dense  of  these  gaseous  mountains  possess 
many  interesting  points  of  structure,  which  can,  and  therefore  in  future  ought  to,  be  perfectly  pre- 
served on  the  photographic  plate;  while  they  prove  that  it  is  only  by  a  very  accurate  timing  of  the 
exposure  that  the  true  form  and  appearance  of  the  more;  delicate  flame-like  prominences  can  hope 
to  be  shown  at  all.  Finally,  they  teach  that,  by  a  judicious  choice  of  the  proper  photographic 
formula?  and  processes  for  this  special  work,  an  impression  of  the  corona  sufficiently  decided  to 
indicate  its  general  features  can  be  obtained  with  an  exposure  that  is  still  not  too  great  for  any 
but  the  very  brightest  of  the  prominences,  thus  rendering  it  possible  to  secure  in  future  on  one 
plate,  even  during  a  totality  of  very  short  duration,  a  valuable  record  of  all  the  phenomena  of  that 
phase  of  an  eclipse. 

In  printing  from  these  negatives  much  of  their  detail  is  lost,  since  they  stand  just  as  they 
cauie  from  the  fixing  bath,  having  been  neither  redeveloped,  intensified,  nor  retouched;  and,  as  a 
consequence,  the  impression  of  the  fainter  portions,  especially  of  the  corona,  is  not  what  a  photo- 
grapher would  call  of  "printing  strength."  But  believing  that  the  relative  intensity  of  the  images 
of  the  various  prominences  and  of  the  corona  was  itself  a  point  of  practical  interest,  I  preferred  not 
to  produce  any  falsification  by  after-intensifying  of  the  plates,  but  to  preserve  the  original  nega- 
tives as  exact  records  of  all  those  phenomena  of  totality  which  it  is  possible  for  photography  to  show. 

There  are  but  two  points  to  be  regretted  in  connection  with  these  negatives.  One  is.  that  the 
first  and  last  few  seconds  of  totality  were  lost  from  the  exposures-,  and  consequently  the  narrow, 
continuous  line  of  the  main  layer  of  the  chromosphere  immediately  surrounding  the  photosphere 
does  not  appear  at  all  in  the  first  plate,  and  only  as  a  mere  trace  in  the  second.  As  will  be  recol- 
lected, the  first  twenty  seconds  of  totality  were  spent  in  struggling  to  see  the  all  lint  invisible 
image  from  the  finder  in  order  to  be  sure  of  the  adjustment  of  the  telescope,  and  the  last  nine  were 
also  lost  because  the  calculated  time  for  the  reappearance  of  the  sun,  as  given  me  by  Professor  Haf- 
ford,  was  between  nine  and  ten  seconds  too  early,  reckoning  by  Professor  Eastman's  rendering  of 
the  actual  time  of  the  third  contact.  The  first  plate,  then,  according  to  the  latter  astronomer's 
observations,  represents  the  appearance  of  the  phenomena  for  sixty -'six  seconds  following  the  twen- 
tieth second  of  duration  of  totality,  and  the  second  for  forty-five  seconds  immediately  preceding 
the  ninth  second  before  the  termination  of  that  phase.  The  other  slight  cause  for  regret  is  that, 
owing  to  the  same  difficulty  in  seeing  the  image  whereby  to  adjust  the  telescope  for  the  second 
plate,  the  centering  on  that  occasion  proves  to  have  been  faulty,  and  the  image,  of  the  moon  in  the 
second  negative  is  a  little  off'  the  field  on  one  side.  But  since  the  portion  so  cut  off'  is  the  south- 
eastern limb,  where  at  the  time  the  negative  was  taken  the  prominences  were  all  covered  by  the 
advancing  moon,  the  mischance  is  of  no  consequence,  except  in  eclipsing  the  image  of  the  south- 
eastern position  wire  and  marring  the  symmetry  of  the  picture  by  the  moon's  lunb,  as  defined  by 
the  corona,  being  lost  for  a  quarter  of  its  extent.  In  this  negative  but  two  of  the  extremities  of 
the  position  wires  are  shown,  namely,  the  north  and  southwestern  ones,  while  on  the  first  plate  all 
four  are  clearly  visible. 

Plates  X  and  XI  are  lithographic  fac-similes  of  these  two  totality  pictures.  The  drawing  on 
the  stone  was  done  under  my  personal  supervision,  and  great  pains  were  taken  that  it  should  be  in 
all  respects  an  accurate  copy  of  the  originals.  But  it  is  impossible  to  reproduce  upon  stone  all  t  In- 
delicate detail  of  these  negatives,  and  the  description  that  follows  is  intended  to  apply  to  Un- 
original photographs  rather  than  to  these  lithographic  plates.  The  latter  represent  the  sun  and 
moon  in  the  position  they  assumed  to  the  naked  e\e  at  DCS  Moines,  the  upper  position  wire  being 
thus  northeast,  the  right-hand  one  northwest,  the  lower  southwest,  and  that  on  the  left  southeast. 

In  studying  the  phenomena  of  the  total  phase  of  the  eclipse  these  photographs  are,  of  course, 
of  great  assistance.  And  though,  so  far  as  the  red  protuberances  are  concerned,  the  genius  of 


OBSERVATIONS    OF    THE    ECLIPSE    OF   AUGUST   7,    1869.  143 

Lockyer,  Janiiseu,  and  lluggins  lias  rendered  it  110  longer  necessary  to  wait  for  a  solar  eclipse  in 
order  to  study  their  form,  structure,  and  constitution,  yet  accurate  photographs  of  the  phenomena 
of  totality  are  still  of  interest,  if  not  value,  as  affording  a  faithful  representation  of  the  peculiar 
features  of  the  corona  and  of  the  appearance  at  a  given  time  of  large  groups  of  protuberances, 
whose  mutual  relations  can  thus  be  more  readily  recognized  than  by  the  plan  of  viewing  the  indi- 
vidual prominences  in  succession  by  means  of  the  spectroscope.  And  such  a  comprehensive  survey 
of  the  combined  appearance  of  the  corona  and  of  groups  of  protuberances  is  of  especial  interest  at  this 
time  in  connection  with  the  important  subject  of  an  outer  solar  atmosphere  beyond  the  layer  of  the 
chromosphere — a  subject  upon  which  the  views  formerly  entertained  have  of  late  been  necessarily 
greatly  modified  by  the  results  of  spectroscopic  observations.  This  means  of  research  has  now  quite 
conclusively  shown  that  the  compound  gaseous  atmosphere  formerly  imagined  to  extend  to  an  im- 
mense distance  from  the  surface  of  the  sun,  and  to  be  the  seat  of  the  absorptive  action  producing  the 
dark  lines  in  the  continuous  spectrum  of  the  photosphere,  does  not  exist  as  supposed,  but  that  this 
action  takes  place  beneath  the  chromosphere.  Moreover,  from  the  known  excessive  tenuity  of  the 
gas  in  the  summits  of  the  red  protuberances,  and  from  its  comparatively  moderate  density  even  in 
the  main  substance  of  the  chromosphere,*  it  follows  that  whatever  gaseous  matter  exists  beyond 
this  envelope  must  be  in  a  state  of  extraordinary  rarefaction. 

Xow  difficult  and  perplexing  though  it  may  be  to  conceive  of  an  atmosphere  that  will  exist 
above  a  layer  of  extremely  rarefied  hydrogen  gas,  yet  the  evidence  afforded  by  these  photographs 
that  the  corona  is  such  an  atmosphere  seems  incontestable.  In  the  lirst  place,  that  this  strange  halo 
cannot  belong  to  the  moon  might  be  considered  sufficiently  certain  from  the  numerous  considera- 
tions that  render  impossible  Hie  existence  of  any  appreciable  lunar  atmosphere.  But  positive  proof 
is  afforded  by  the  two  photographs,  which,  when  compared  together,  show  unmistakably  that  in 
August  last  the  corona -was  progressively  eclipsed  by  the  ad  vaneing  moon  precisely  as  were  the 
protuberances.  In  the  second  place,  the  notion  that  the  corona  may  be  the  luminosity  of  our  own 
sun-lit  atmosphere  beyond  the  belt  of  totality  is  also  both  theoretically  impossible  and  practically 
proven  false  by  the  testimony  of  the  photographs.  As  to  the  theoretical  considerations,  it  is  suffi- 
cient to  point  out  that  with  the  diameter  of  the  moon's  shadow  upon  the  earth  twice  or  three  times 
as  great  as  the  vertical  extent  of  our  own  atmosphere,  it  is  geometrically  impossible  for  an  observer 
near  the  center  of  that  shadow  to  see  any  portions  of  our  atmosphere  which  lie  beyond  the  cone  of 
darkness — which  portions  alone,  of  course,  could  under  the  circumstances  be  illuminated — in  appa- 
rent contiguity  with  the  moon's  limb.  This  illumination  of  the  earth's  atmosphere,  could  it  take  the 
form  of  a  distinct  halo,  resembling  the  corona  at  all,  would  necessarily  appear  as  an  immense  ring  of 
light  in  the  heavens,  altering  its  apparent  relative  position  with  respect  to  the  moon,  as  the  latter 
body  advanced  in  its  transit  over  the  sun.  Theory  alone,  then,  would  force  us  to  the  conviction 
that  the  corona  must  belong  to  the  sun ;  but,  as  previously  stated,  positive  evidence  pointing  in  the 
same  direction  seems  to  be  afforded  by  the  photographs,  in  the  fact  that  they  show  an  unmistakable 
relationship  bctirrcn  i-orona  anil  protuberances,  the  corona  being  markedly  deficient  immediately  over 
those  prominences  where  the  substance  of  the  chromosphere  has  been  heaped  up  into  apparent  solid 
nodules,  and  markedly  brilliant  in  and  among  the  closely  grouped  protuberances  composed  of  long 
waving  tongues  and  small  detached  masses  of  gaseous  matter.t  These  peculiarities  of  the  corona 
were  quite  generally  noticed  by  the  eye-observers  also  at  DCS  Moines,  where  the  brilliancy  of  the 
corona  light  was  dimmed  by  the  haze;  but  I  can  readily  conceive  that  in  a  clearer  atmosphere  they 
would  not  be  so  apparent,  since  from  the  great  depth  of  corona  looked  through,  the  total  visual 
luminosity  along  a  given  line  of  sight  might  be  so  great  that  a  considerable  excess  or  deficiency  of 
brilliancy  for  a  space  of  but  limited  extent  along  this  line  might  be  relatively  too  slight  to  be 
detected  upon  viewing  the  corona  as  a  whole.  In  the  photograph,  however,  where  the  total  effect  is 

*  Frankliiml  and  Lockyer.    Proceedings  of  the  Royal  Society,  Vol.  XVII,  No.  109,  pp.  289,  290. 

t  The  lithographic  fac-simile  of  the  first  totality  picture  (I'l ate  X)  while  giving  a  faithful  representation  of  the 
intensity  and  general  extent  of  the  corona,  us  shown  by  the  photograph,  I  am  sorry  to  find  fails,  in  printing,  to  show  the 
irregularities  of  its  outline.  The  corona  should  appear  almost  alisent  in  a  direction  towards  the  right-hand  upper 
corner  of  the  plate,  and  should  show  a  marked  converging  burst  of  light  exactly  towards  the  right-hand  side  of  the 
picture.  In  and  among  the  group  of  protuberances  embracing  Hie  "  T,"  the  corona  light  should  also  appear  much 
stronger  than  the  lithograph  represents  it.  Plate  XI  (fac-simile  of  the  second  totality  photograph)  is,  however,  very 
faithful  in  its  representation  of  (he  corona. 


144  REPORT   OF   DR.  CURTIS. 

but  faiut,  these  variations  iu  the  coronal  brightness  in  the  plane  of  the  great  circle  of  the  solar 
sphere  normal  to  the  line  of  sight  become  readily  manifest.  Other  irregularities  in  the  features  of 
the  corona,  incompatible  with  the  notion  of  its  being  a  phenomenon  of  our  own  atmosphere,  are 
shown  by  the  photographs,  namely,  a  converging  bundle  of  rays  stretching out  to  the  northwest,  and, 
what  especially  points  to  the  corona's  being  an  envelope  of  the  sun,  a  well  marked  deficiency  of  the 
halo  in  the  neighborhood  of  the  solar  poles.*  And  still  more  conclusive  than  any  of  these  photo- 

*  Since  writing  the  above,  I  have  read  with  considerable  surprise  an  extract  from  a  letter  of  Dr.  B.  A.  Gould  to 
Professor  Henry  Morton,  of  the  Franklin  Institute  of  Philadelphia,  published  in  t  he  current .October  number  of  the 
journal  of  that  institute,  (page  222)  in  which  Dr.  Gould  says  :  "  An  examination  of  the  beautiful  photographs  made  at 
Burlington  and  Ottnmwa  by  the  sections  of  your  party  in  charge  of  Professors  Mayer  and  Hiiues.  and  a  comparison  of 
them  with  my  sketches  of  the  corona,  have  led  me  to  the  conviction  that  the  radiance  around  the  moon,  in  the  pictures 
made  during  totality,  is  not  the  corona  at  all,  but  is  actually  the  image  of  what  Lockyer  has  called  the  chromosphere." 
Dr.  Gould  proceeds  to  specify  the  points  at  variance  between  the  corona  as  photographed  and  the  same  object  as  seen 
and  sketched  b\  him,  and  because  the  two  representations  do  not  correspond  in  feature  he  infers  that  the  objects 
depicted  cannot  be  identical.  This  same  argument  would  apply  equally  well  to  the  '•  radiance"  shown  in  my  own  photo- 
graphs, since  in  them  the  phenomenon,  though  faint,  agrees  in  outline  with  the' similar  object  on  the  Burlington  and 
Ottnmwa  pictures. 

Now  I  cannot  but  believe  that  Dr.  Gould  is  in  error  in  imagining  this  aureole  not  to  be  simply  the  image  of  the 
more  intense  portion  of  the  corona  near  the  surface  of  the  sun.  In  the  first  place  the  experience  of  this  very  eclipse 
has  shown  how  guardedly  all  sketches  and  drawings  of  the  appearances  of  totality  should  be  receh  ed  as  a  Hording  an 
accurate  record  of  either  the  shape,  size,  or  position  of  the  various  objects.  This  is  evident  upon  comparing  the  various 
sketches  made  by  eye  observers  of  the  protuberances  and  corona,  both  with  each  other  and  with  the  photographs,  and 
observing  the  very  great  discrepancies  manifest.  Of  course  it  is  not  meant  that  accurate  measurements  made  by  a 
micrometer  eye-piece  in  the  telescope  or  similar  determinations  of  position  angle  cannot  be  relied  upon,  but,  on  the  con- 
trary, the  argument  is  that  only  such  are  to  be  received  as  trustworthy, and  that  all  yi-wraJ  sketches  and  drawings  made 
hastily  during  the  few  exciting  minutes  of  totality,  or  from  memory  afterward,  form  but  a  weak  ground  upon  which  to 
base  an  important  scientific  hypothesis.  But  positive  proof  in  the  question  a  I  issue  is  atlbrded  by  the  very  perfect  photo- 
graphs of  the  corona  taken  at  Shelbyville,  Kentucky,  by  Mr.  AYhipple,  of  the  Cambridge  expedition.  Here  we  have  a  series 
of  several  negatives  obtained  by  receiving  the  focal  image  of  a  six-inch  object-glass  directly  upon  the  sensitive  plate, 
and  taken  with  a  wide  range  of  exposures  from  five  to  forty  seconds.  Of  these  the  one  exposed  the  longest  yields  a 
splendid  and  unmistakable  picture  of  the  corona,  representing  it.  where  the  converging  rays  occurred,  of  a  depth  equal 
to  a  quarter  of  the  moon's  diameter.  Surely  Dr.  Gould  c: of  imagine  the  aureole  of  thi*  photograph  to  be  the  chro- 
mosphere and  not  the  corona,  and  yet  all  of  these  pictures  of  Mr.  Whipplc's,  ami  nil  of  the  Philadelphia  expedition,  and 
my  own  agree  perfectly  in  the  features  and  position  of  the  \  arions  irregularities  in  the  outline  of  the  corona,  the  differ- 
ence in  the  representation  of  that  object  in  the  several  photographs  being  solely  one  of  extent  and  brilliancy.  Dr. 
Gould  adduces  as  an  additional  argument  in  favor  of  his  assumption  the  observation  that  the  long  coronal  beams, 
appeared  to  him  to  be  "variable."  while  the  "  aureole"  photographed  was  evidently  "  constant"  during  t  he  time  of  totality. 
This  argument,  however,  loses  some  of  its  force  when  it  is  remembered  thai  to  other  observers  the  corona  appeared  to 
the  eye  absolutely  unchangeable,  both  in  form  and  position,  during  the  whole  period  of  the  total  obscuration. 

Perhaps  Dr.  (Jould, since  he  based  hisbypothesis  upon  an  examination  of  the  photographs  taken  by  the  Philadelphia 
expedition,  was  influenced  in  forming  the  opinion  he  has  advanced  by  the  fact  that  upon  these  photographs  the 
"aureole,"  while  falling  far  short  of  the  height  above  the  moon's  limb  attained  liy  the  corona,  as  seen  by  the  eye,  yet 
appears  of  very  great  brilliancy,  rivaling  the  protuberances  in  that  respect,  and  comes  to  almost  an  abrupt  termination 
a  short  distance  above  the  solar  surface.  Comparing,  therefore,  1>riUiiiii<-//  with  rjrteut,  Dr.  Gould  may  have  taken  the 
disagreement  in  these  respects  between  the  corona  as  photographed  and  as  seen,  to  afford  an  additional  argument  in 
favor  of  the  idea  that  in  the  former  case  the  aureole  represented  could  not  be  the  corona  at  all.  lint  as  a  fact  this  great 
and  rather  undue  brilliancy  of  the  corona,  considering  its  extent,  in  the  photographs  described,  is  probably  altogether  a  pho 
tographic  effect,  such  prints  of  the  Burlington  andOttumwa  pictures  as  I  have  seen  giving  every  indication  that  the  nega 
lives  from  which  they  were  taken  were  strongly  intensified  after  fixing.  This  Operation,  practiced  to  give  additional  den- 
sity to  weak  negatives,  would  have,  in  this  case,  precisely  the  effect  of  increasing  on  the  photograph  the  apparent  brilliancy 
of  the  corona,  without  adding  to  its  extent.  Moreover,  that  this  excessive  photographic  brilliancy  of  the  under  portion 
of  the  corona  should  not  be  taken  as  a  proof  of  any  physical  or  chemical  peculiarity  in  the  actual  object  is  quite  con- 
clusively proved  by  my  own  photographs,  which,  while  showing  about  the  same  extent  of  corona  as  those  pictures  of 
the  Philadelphia,  party  that  received  the  least  exposure,  yet  represent  it  as  a  very  feeble  luminosity,  fading  gradually  anil 
imperceptibly  into  complete  darkness,  and  this  while  the  same  photographs  show  the  protuberances  of  great  brilliancy. 

If  this  peculiarity  of  the  Burlington  and  Ottumwa  photographs  had  indeed  any  influence  in  leading  Dr.  Gould  into 
the  misconception  into  which  I  cannot  but  believe  lie  has  fallen,  the  circumstance  affords  but  another  example  among 
many  that  I  have  seen,  of  the  necessity  that  a  critic,  before  attempting  to  draw  scientific  inferences  from  photographic 
representations,  should  himself  become  something  of  a  photographer,  else  hi-  will  be  very  apt  to  fall  into  this  natural 
error  of  ascribing  effects  wholly  produced  in  the  dark-room  to  physical  characteristics  of  the  object  portrayed.  And, by 
B  singular  coincidence,  evidence  that  Or.  Gould  has  not  a  practical  acquaintance  with  the  art  would  seem  to  be  afforded 

iu  this  same  published  letter  by  his  total  misinterpretation  of  another  purely  photographic  effect,  viz:  the  apparent 
encroachment  of  the  prominences  upon  the  disk  of  the  moon  as  seen  in  the  photographs.  This  curious  appearance, 
instead  of  being  due  to  "  specular  reflection,"  is  wholly  a  dark-room  phenomenon,  as  will  be  explained  in  the  text. 


1869.  145 

graphic  indications  is  the  testimony  of  the  spectroscope,  which  in  the  hands  of  Professor  Harkness 
gave  for  the  corona  a  continuous  spectrum  with  no  indication  of  the  Fraunhofer  lines,  and  in  addi- 
tion one  bright  line. 

In  view  of  the  above  adduced  evidence,  then,  we  seem  warranted  in  considering  it  quite  cer- 
tain that  the  corona  belongs  to  the  sun,  and  there  appears  at  present  no  escape  but  to  assume  it  to 
represent  an  extremely  rarifted  atmosphere  above  the  hydrogen  envelope  of  the  chromosphere. 
Pending,  then,  the  results  of  future  researches  upon  this  mysterious  and  almost  impalpable  gaseous 
atmosphere,  it  is  well  to  search  for  such  circumstantial  evidence  as  to  its  existence  and  its  physical 
conditions  as  may  be  afforded  by  the  aspect  of  the  underlying  solar  prominences ;  for  it  is  evident 
that  these  by  their  appearance  should  indicate  whether  the  gaseous  medium  that  surrounds  them 
is  of  such  extreme  tenuity  and  subject  to  such  sluggish  motions  only  as  to  be  practically  powerless 
to  affect  by  its  pressure  and  currents  their  rapidly  changing  forms,  or  whether,  on  the  other  hand, 
this  atmosphere,  rare  as  it  must  be,  is  yet  of  sufficient  density  and  the  seat  of  sufficiently  violent 
winds  to  palpably  blow  the  light  matter  composing  the  chromosphere  before  it,  and  to  be  thus  one 
of  the  agencies  in  producing  the  peculiar  and  phantastic  shapes  which  the  protuberances  from  the 
surface  of  this  gaseous  envelope  frequently  assume. 

Now  in  studying  the  aspect  of  the  prominences,  as  shown  by  the  photographs,  with  this 
object  in  view,  it  is  impossible  not  to  be  struck  with  the  fact  now  quite  generally  noticed  in  obser- 
vations of  the  protuberances,  that  these  bodies  are  unquestionably  produced  at  the  outset  by  the 
action  of  forces  from  within  or  beneath  the  gaseous  envelope  of  the  chromosphere  itself — that  they 
are  upheavals,  in  other  words,  and  not  in  any  respect  waves  upon  the  gaseous  sea  blown  into  exist- 
ence by  winds  of  an  outer  atmosphere.  This  appearance  of  upheaval  is  perhaps  most  strikingly 
manifest  in  the  magnificent  prominence  seen  at  the  under — southwestern — border  of  the  moon, 
which,  from  its  size  and  splendor,  has  been  universally  called  the  "great  protuberance."  On 
examining  this  in  the  second  totality  photograph,  holding  the  plate  so  that  the  prominence  shall 
be  uppermost,  it  will  be  seen  to  closely  resemble  in  character  a  bubbling  spring,  or  a  fountain 
whose  discharge  pipe  terminates  a  little  below  the  surface  of  the  water.  There  is  the  same  appear- 
ance of  vast  volumes  of  matter  tossed  up  into  an  irregular  heap  by  the  ejecting  force  and  sinking 
back  again  on  all  sides  in  long  vertical  rolls.  Four  such  down-pouring  streams  of  gas  are  visible 
in  this  fiery  fountain,  two  of  apparently  greater  density,  because  viewed  directly  from  the  front, 
flowing  toward  the  observer,  and  the  others,  one  to  each  side,  leaving  a  clear  space  between  their 
under  surfaces  and  the  main  layer  of  the  chromosphere,  which,  reaching  right  and  left  from  the 
central  streams,  is  just  visible  as  a  narrow  lino  above  the  limb  of  the  dark  moon.  It  would  seem 
that  in  this  case  the  upheaving  force  was  directed  obliquely  to  the  right,  (the  photograph  being 
still  held  upside  down,)  and  was  also  advancing  in  the  direction  of  its  slant,  since  the  middle 
streams  roll  down  with  a  little  inclination  to  the  left,  the  right-hand  one  is  sharply  bent  as  if  by 
the  main  mass  of  the  protuberance  pressing  against  it  from  behind,  and  that  on  the  left  is  trailed 
off  into  a  beautiful  long  streamer  of  considerable  tenuity,  which,  finally  breaking  up  into  little 
detached  masses,  sinks  down  until  lost  behind  the  body  of  the  moon,  the  appearance  being  not 
unlike  the  long  trail  of  smoke  from  a  locomotive.  Xorth.  of  this  great  fountain  protuberance  is  a 
group  aptly  named  by  some  one  the  antelope  horns,  which  exhibits  no  less  markedly  their  formation 
by  ejection  from  the  gaseous  stratum  below.  Here,  ho\vevcr,  the  matter  would  seem  to  have  been 
forced  up  in  a  double  narrow  column,  of  which  one  at  least  was  possessed  also  of  a  spiral  motion, 
since  the  north  "horn"  still  shows  a  distinct  spiral  twist,  perfectly  visible  in  the  photograph. 
These  two  columns,  falling  apart,  are  seen  sinking  back  to  the  surface  of  the  sun  in  opposite  direc- 
tions. Beyond  this  group  again,  still  in  the  second  photograph,  is  a  bright  prominence  strongly 
suggestive  of  the  action  of  a  sudden  and,  as  it  were,  explosive  force,  the  gas  flaming  out  in  all 
directions  from  one  point  of  greater  intensity  close  down  to  the  border  of  the  moon,  the  whole 
looking  like  the  bursting  upward  of  a  bombshell. 

On  the  first  totality  plate  there  are  visible,  beside  the  great  fountain  protuberance,  two  others 
of  massive  character,  one  of  them,  surmounted  by  two  short  tails  or  streamers,  bearing  a  rude 
resemblance  to  the  head  of  some  of  the  long-eared  varieties  of  owls.  The  appearance  of  this 
prominence  suggests  the  idea  that  it  is  rotating  on  a  vertical  axis.  Xeither  of  these  protuber- 
ances presents  any  striking  features,  so  we  may  pass  at  once  to  the  main  object  of  interest  in  this 
19* 


146  REPORT    OF   DR.    CURTIS. 

picture,  namely,  a  group  of  delicate,  phantastic  name-like  prominences,  extending  along  the  eastern 
limb  of  the  sun  for  a  distance  of  35°,  and  shown  in  the  photograph  with  exquisite  beauty.  The 
most  southerly  of  these  bears  a  striking  resemblance  to  a  capital  T,  the  cross-piece  being  entirely 
detached  from  the  main  shaft  and  curved  with  the  concavity  toward  the  sun.  This  prominence 
looks  precisely  as  if  it  were  the  eifect  of  a  sudden  spirting  of  gas  ejected  directly  upwards  from 
the  surface  of  the  chromosphere,  of  which  the  top  of  the  column,  its  force  being  spent,  is  rolled 
into  a  huge  ring,  like  the  rings  of  smoke  from  a  locomotive,  and  is  slowly  settling  back.  It  is  very 
like  many  of  those  figured  by  Professor  Zollner,  as  seen  by  him  in  his  spectroscope.*  Immediately 
beyond  this  prominence  is  another  long,  narrow  wisp  of  gaseous  matter  curling  to  the  north  and 
ending  in  three  detached  masses,  which,  having  apparently  floated  oft'  from  the  end  of  the  wisp, 
seem  to  be  falling  back  to  the  sun.  The  whole  suggests  the  appearance  of  a  rocket  just  burst, 
when  the  stars  and  the  long  curved  tail  are  both  slowly  sinking  to  the  earth.  Next  to  this  rocket 
occurs  a  confused  mass  of  rolling  flames  of  gradually  decreasing  height,  which  look  as  if  they  too 
had  been  previously  waving  in  long  tongues,  but  were  now  bowed  down  and  rolled  into  a  heap 
together.  Beyond  them,  in  the  middle  of  a  space  almost  devoid  of  corona,  stands  the  most  inter- 
esting of  all  the  protuberances  seen  during  the  eclipse.  It  is  composed  of  a  narrow  tapering  body 
inclined  to  the  sun's  surface  at  an  angle  of  45°  toward  the  north,  and  terminating  in  three  long, 
widely  divergent  streamers.  The  body  tapers  to  the  finest  point,  where  it  apparently  touches  the 
lunar  disk,  and  contains  four  nodules  of  greater  density  symmetrically  arranged.  Of  the  stream- 
ers, one  starting  from  the  upper  surface  of  the  body  as  it  stands  inclined,  passes  vertically  upward 
a  short  distance  and  then,  bending  sharply  down  almost  at  a  right  angle,  sweeps  off  to  the  south. 
The  two  others,  the  middle  and  brightest  one  of  the  three  being  a  continuation  of  the  main  body, 
follow  the  general  direction  of  the  latter  toward  the  north  while  curving  gradually  downward. 
All  three  in  their  final  course  are  very  nearly  parallel  to  each  other,  and  would,  if  prolonged  north- 
ward, meet  the  surface  of  the  sun  at  a  very  acute  angle.  From  the  striking  resemblance  which 
this  curious  protuberance  bears  to  an  ear  of  Indian  corn  as  seen  growing  iipon  the  stalk  with  the 
long  points  of  the  husks  waving  in  the  wind,  I  have  given  it  that  name.  Beyond  it  are  two  long 
curved  tongues  of  gas  arching  sharply  to  the  south. 

Now,  on  viewing  as  a  whole  the  extraordinary  group  of  prominences  just  described,  it  would 
seem  that  here,  in  exception  to  the  indications  from  the  other  protuberances  studied,  there  is 
afforded  circumstantial  evidence,  such  as  it  is,  of  the  action  of  a  local  current  of  some  gaseous 
medium  of  sufficient  density  to  be  able  to  bear  down  the  substance  of  the  prominences  before  it. 
The  current  thus  indicated  is  in  the  form  of  a  gigantic  whirlwind  upon  the  surface  of  the  chromo- 
sphere, with,  a  sweep  over  two  hundred  thousand  miles  in  diameter  around  the  corn-ear  protuber- 
ance as  an  axis.  The  indications,  which  are  numerous,  striking,  and  concordant,  are  as  follows:  In 
the  first  place,  with  reference  to  the  corn  ear  itself,  it  is  difficult  not  to  believe  that  this  prominence 
as  represented  in  the  photograph  is,  from  whatever  cause,  rapidly  rotating,  since  the  supposition 
of  such  a  motion  is  by  far  the  most  natural  and  simple  way  of  accounting  for  the  fusiform  shape  of 
the  body  and  the  coexistence  of  the  widely  divergent  streamers,  which'  have  precisely  the  aspect 
of  being  whirled  off  from  the  main  mass  by  the  action  of  centrifugal  force.  As  a  cause  for  this 
axial  rotation,  the  first  conjecture  would  naturally  be  that  the  prominence,  like  all  that  have  been 
already  studied,  is  a  mass  of  glowing  gas  that  has  been  projected  upward  from  the  surface  of  the 
chromosphere,  only  here  with  unusual  violence,  and  with  an  accessory  screwing  motion,  which  has 
imparted  to  the  mass  a  rotation  visible  at  its  summit,  where  the  force  of  propulsion  has  ceased,  by 
the  whirling  off  of  portions  of  gaseous  matter.  This  supposition,  however,  which  would  hold  good 
were  the  prominence  isolated  upon  the  surface  of  the  sun,  does  not  account  so  well  for  the  aspect 
of  the  rest  of  the  group,  of  which  it  is  the  central  figure,  as  the  hypothesis  that  the  mass  owes  its 
present  form  and  spinning  motion  to  its  being  a  passive  victim  in  the  vortex  of  a  mighty  tornado. 
The  indications  of  the  whirlwind  afforded  by  the  other  members  of  the  group  are  to  be  found,  first, 
in  the  appearance  of  the  two  long  wisps  of  gas  north  of  the  corn  ear,  which  unmistakably  owe  their 
form  and  position  to  the  same  force  that  is  acting  upon  that  prominence;  secondly,  in  the  aspect 
of  the  rolling  masses  of  flame  to  the  south,  which  appear  to  be  borne  down  by  some  force  whose 
action  extends  obliquely  outward  in  a  straight  line  from  the  base  of  the  corn  ear,  and  very  nearly 

*  Astrouomische  Nacliricbten,  Bd.  74,  No.  1769. 


OBSERVATIONS    OF   THE    ECLIPSE    OP   AUGUST   7,    18G9.  147 

parallel  to  the  direction  of  the  long  southerly  streamer  from  the  same.  Finally,  evidence  is  afforded 
by  the  total  absence  of  any  loose  wisps  of  gas  in  the  bare  spot  upon  which  the  latter  protuberance 
is  reared. 

STow,  in  order  to  understand  exactly  the  value. of  the  indications  thus  pointed  out,  let  us  assume 
a  whirlwind,  and  deducing  what  would  be  its  natural  effects,  observe  how  they  correspond  with 
the  actual  appearances  manifest  in  the  photograph.  In  the  first  place, .it  is  not  unnatural  to  imag- 
ine that  the  violent  bubbling  action  in  the  chromosphere,  producing  the  group  of  flames  containing 
the  "T"  and  tho  rocket,  extended  originally  along  the  whole  arc  between  those  protuberances  and 
the  wisps  beyond  the  corn  ear.  Let  us  then  assume  the  generation,  .in  the  center  of  this  troubled 
mass,  of  a  whirlwind,  shallow  in  depth  but  of  great  lateral  extent.  Such  a  tornado  would  naturally 
catch  up  all  the  flickering  tongues  of  gas  within  its  grasp,  suck  them  into  its  vortex,  and  there  mold 
them  into  precisely  such  a  tapering  and  whirling  mass  as  the  body  of  the  corn  ear  presents.  The 
top  of  this  gaseous  column  then  being  finally  carried  above  the  level  of  the  whirlwind,  its  outer 
layer  would  be  swung  off  by  centrifugal  force  into  just  such  long  trailing  streamers  as  are  actu- 
ally found  to  diverge  from  the  summit  of  this  prominence.  Beneath  the  whirlwind  we  should 
expect  everything  not  sucked  into  its  vortex  to  be  blown  flat,  and  we  accordingly  find  the  surface 
of  the  chromosphere  for  a  wide  extent  around  the  base  of  the  corn  ear  absolutely  level,  while  the 
flaring  flames  to  the  south  are  bowed  down  into  a  confused  heap,  where  they  impinge  upon  the  under 
surface  of  the  tornado.  And  this  surface,  as  thus  sharply  defined,  by  the  line  bounding  the  summit 
of  the  mass  of  rolling  flames,  will,  when  the  real  position  of  the  hidden  sun  on  the  photograph  is 
taken  into  account,  be  found  to  be  almost  exactly  tangential  to  the  solar  surface  at  a  point  a  little 
north  of  the  corn  ear,  and  very  nearly  parallel  with  the  upper  surface  of  the  whirlwind,  whose 
direction  is  clearly  indicated  by  means  of  the  streamers  from  the  above-mentioned  prominence. 
The  upper  and  lower  surfaces  of  the  eddy,  however,  converge  slightly  toward  the  north,  and  if 
we  assume  the  limit  of  the  tornado  in  that  direction  to  be  reached  while  its  sweep  is  yet  within  the 
tumultuous  hearings  of  the  chromosphere,  we.  should  again  anticipate  precisely  the  appearance 
actually  shown  in  the  photograph.  We  should  expect,  that  is,  that  the  loose  bodies  of  gas  near  the 
border  of  the  storm  would  be  caught  by  the  gigantic  eddy,  and  whirling  around  upon  its  outer  sur- 
face, would  be  drawn  out  into  long,  curved,  trailing  streamers,  densest  at  the  base  where  still  cling- 
ing to  the  surface  of  the  chromosphere,  most  tenuous  at  the  tips  where  spun  out  into  a  condition  of 
extreme  rarefaction  by  the  sweeping  current.  And  nothing  could  be  more  perfect  than  the  realiza- 
tion of  these  anticipated  effects  in  the  two  long  tongues  of  gas  seen  in  the  photograph  north  of  the 
corn  ear.  The  curve  of  their  sweep  is  probably  foreshortened  by  perspective,  but  it  will  be  at  once 
observed  that  their  tips  point  exactly  toward  the  tips  of  the  two  northerly  streamers  from  the 
above-mentioned  prominence,  clearly  indicating  that  all  are  borne  upon  the  surface  of  the  same 
mighty  current. 

Here,  then,  we  luive  the  case  of  a  group  of  striking  phenomena,  and  a  hypothesis  that  seems 
to  fully  and  naturally  account  for  them  all.  But  even  if  we  assume  upon  the  strength  of  these 
indications  that  a  whirlwind  actually  existed  as  imagined,  the  question  of  what  was  the  substance 
that  composed  the  wind  is  still  an  open  one.  Two  suppositions  are  possible:  one,  that  the  tornado 
was  a  current  in  the  gaseous  atmosphere  of  the  corona,  and  the  other  that  it  was  an  eddy  composed 
of  the  matter  of  the  chromosphere  itself  cooled  below  the  point  of  luminosity.  Such  an  eddy  might 
readily  be  accounted  for  as  follows:  We  have  evidence  in  the  "T,"  the  rocket,  and  the  corn  ear 
prominences  that  the  chromosphere  was  in  this  region  before  the  time  of  the  eclipse,  in  a  state  of 
unusually  violent  agitation,  the  gases  being  ejected  upward  in  vast  volumes  and  to  great  heights. 
Such  masses,  after  the  ejecting  force  is  spent  and  they  become  cooled  by  radiation,  must  contract 
and  gravitate  back  to  the  surface  of  the  parent  layer  in  currents  of  considerable  strength.  In  the 
present  case,  then,  where  the  outpouring  of  the  glowing  hydrogen  had  been  unusually  violent  and 
extensive,  it  is  not  unnatural  to  suppose  that  the  subsequent  tumultuous  downrush  of  the  cooling 
gas  should,  from  local  causes,  have  taken  on  an  eddying  motion,  thus  giving  rise  to  the  appearance 
of  a  whirlwind  of  which  the  main  substance  could  not  be  seen  because  cooled  below  the  point  of 
luminosity,  but  the  heart,  retaining  as  yet  its  heat,  remained  visible  as  the  singular  corn  ear  pro- 
tuberance. 

Whichever  supposition  as  to  the  constitution  of  the  imaginary  whirlwind  may  be  correct,  it  is 


148  REPORT   OF   DR.    CURTIS. 

important  to  observe  that  at  the  limits  of  its  supposed  sweep  the  photographs  show  the  luminous 
corona  to  conie  to  an  abrupt  termination,  although  immediately  beyond,  in  the  groups  of  flaring 
prominences  adjoining,  the  light  of  this  phenomenon  is  brighter  than  at  any  other  point.  This  fact, 
which  gives  additional  strength  to  the  hypothesis  of  the  existence  within  those  limits  of  a  violent 
wind,  shows  what  would  a  priori  be  expected,  that  the  gaseous  substance  of  this  wind  was  com- 
paratively cool.  Another  point  of  interest  is  that  the  corn  ear  protuberance,  and  therefore  the 
vortex  of  the  supposed  whirlwind,  were  quite  close  to  the  sun's  equator,  and  were  also  in  the  neigh 
borhood  of  a  large  sun-spot  and  group  of  bright  facula>.  Photographs  of  the  sun  were  taken  for 
two  days  succeeding  the  eclipse,  to  see  if  any  additional  sun-spots  would  appear  whose  position 
might  have  been  nearer  that  of  the  corn-ear  prominence;  none  such,  however,  were  to  be  found, 
although  a  second  group  of  facula>  was  brought  into  view,  whose  position  on  the  day  of  the  eclipse 
must  have  been  coincident  with  that  of  the  group  of  protuberances  containing  the  "T"  and  the  rocket. 
Our  analysis  of  the  appearance  of  the  red  protuberances  as  exhibited  in  the  photographs,  results, 
therefore,  in  the  finding  that  at  only  one  point  is  there  any  marked  indication  of  these  bodies  being 
acted  upon  by  atmospheric  currents,  and  that  here,  from  the  fact  that  the  supposed  aerial  move- 
ment was  a  local  eddy  occurring  in  the  heart  of  an  unusually  tumultuous  outpouring  of  the  gas  of 
the  chromosphere,  it  is  possible  that  the  current  should  be  interpreted  as  an  eddying  motion  of 
cooled  masses  of  this  substance  itself,  and  not  of  the  rarefied  atmosphere  supposed  to  be  represented 
by  the  corona.  But,  however  all  this  may  be,  it  is  evident  from  the  striking  character  of  the  pro- 
tuberances shown  in  the  photographs  that  much  may  be  learned  from  systematic  observations  of 
the  form  and  manner  of  growth  and  dissolution  of  groups  of  these  bodies,  and  it  is  to  be  hoped 
that,  following  the  proposal  of  Zollner,  those  having  such  observations  in  charge  will  make  use  of 
photography  to  record  the  fleeting  forms.  This  could  easily  be  done,  and  photographs  of  interesting 
prominences  taken  at  short  intervals  during  their  ephemeral  existence  by  attaching  a  small  camera 
to  the  spectroscope,  widening  the  slit  of  the  latter,  and  receiving  upon  the  sensitive  plate  the 
image  formed  by  the  rays  of  the  blue  hydrogen  line  in  the  spectrum  of  those  gaseous  bodies. 

The  question  of  whether  during  this  eclipse,  as  on  the  occasion  of  that  of  I860,  there  were  any 
protuberances  whose  light  Avas  of  so  much  greater  photographic  than  visual  intensity  that  they 
would  impress  themselves  on  a  negative  while  invisible  to  the  eye,  it  is  premature  to  attempt  to 
answer  in  this  place.  This,  with  the  converse  question,  whether  any  protuberances  were  seen 
which  do  not  appear  upon  the  photographs,  must  be  settled  by  the  eye-observers  themselves  upon 
an  inspection  of  the  plates.  It  is  well,  however,  to  give  the  caution  that  in  considering  the  photo- 
graphs due  allowance  must  be  made  for  the  facts  that  the  exposures  did  not  include  the  first  twenty 
nor  the  last  nine  seconds  of  totality,  and  that  the  observatory  at  DCS  Moines  was  some  distance 
southwest  of  the  central  line  of  the  shadow. 

An  examination  of  the  solar  negatives  taken  on  days  previous  and  subsequent  to  the  day  of 
the  eclipse  fails  to  show  any  immediate  connection  between  sun-spots  and  protuberances.  Of  all 
the  sun-spots  visible  on  the  4th,  7th,  8th,  and  9th  of  August  none  could  have  been  in  the  neigh 
borhood  of  any  of  the  prominences  visible  during  the  eclipse,  except  the  large  spot  previously  men- 
tioned as  being  quite  near  the  corn  ear  protuberance.  There  is  merely  the  coincidence  to  note  that 
all  the  large  sun-spots  visible  between  the  26th  of  July  and  the  9th  of  August,  (the  period  over 
which  the  solar  negatives  extend,)  were,  with  a  single  exception,  on  the  southern  hemisphere  of  the 
sun ;  and  that  during  the  eclipse  the  majority  of  the  protuberances,  according  to  the  photographs, 
were  upon  the  same  hemisphere.  Here  again,  however,  allowance  must  be  made  for  the  position  of 
the  post  of  observation  south  of  the  central  line  of  shadow.  Of  faculce  the  solar  negatives  show 
an  abundance,  and  prove  that  there  must  have  been  almost  a  continuous  line  of  these  objects  along 
that  portion  of  the  circumference  of  a  great  circle  of  the  solar  sphere  occupied  by  the  protuber- 
ances during  the  total  phase  of  the  eclipse. 

On  the  question  of  whether  there  was  any  perceptible  motion  in  the  prominences  during  the 
three  minutes  of  totality,  the  photographs,  on  account  of  the  excessively  long  exposures  that  had 
to  be  given  the  plates,  unfortunately  cannot  speak.  The  great  fountain  protuberance  and  the 
extreme  tips  of  the  uppermost  streamers  from  the  corn  ear  are  the  only  two  of  these  bodies  depicted 
on  both  of  the  plates,  and  it  can  merely  be  said  that  they  show  no  signs  of  any  perceptible  motion 
having  taken  place  during  the  time  of  the  total  obscuration  at  Ues  Moines. 


1869.  149 

A  point  of  considerable  interest  and  practical  importance  in  connection  with  the  totality  pic- 
tures yet  remains  to  be  discussed.  In  the  photographs  obtained  by  l)e  La  Eue  in  I860,  and  by 
Vogel  iu  18GS,  there  is  noticeable  a  marked  irregular  rounding  of  the  contour  of  all  the  prominences, 
even  on  the  side  adjoining  the  sun,  giving  them  a  more  or  less  beaded  and  sausage-like  aspect, 
Combined  with  this  there  is  also  an  apparent  encroachment  of  their  under  edges  upon  the  disk  of 
the  moon,  apart  from  the  spurious  effect  of  this  nature  produced  by  the  progressive  motion  of  the 
moon  during  the  exposure  of  the  plates  in  the  telescope.  These  curious  appearances  have  been 
variously  commented  upon  from  time  to  time;  some  even  imagining  the  rounding  of  the  under 
edges  of  the  protuberances  to  indicate  that  these'bodies  are  all  separated  by  a  narrow  space  from 
the  solar  surface  beneath,  and  that  they  must  therefore  be  considered  as  cloud-like  masses  floating 
free  in  the  solar  atmosphere.  Such  a  supposition,  however,  fails  to  account  for  the  encroachment 
of  the  image  of  the  prominences  upon  the  lunar  disk,  and  is  totally  at  variance  with  the  positive 
knowledge  we  now  possess  that  the  chromosphere  forms  a  continuous  envelope  around  the  sun,  and 
that  the  red  protuberances  are  merely  irregular  upheavings  of  its  gaseous  substance,  which  only 
exceptionally  become  detached  in  any  large  mass  from  the  parent  layer.  Being  satisfied  that  the 
true  explanation  of  the  appearances  described  was  yet  to  be  found,  I  inspected  my  own  negatives 
after  the  eclipse  was  over,  with  considerable  curiosity,  to  see  what  light  they  would  throw  on  the 
subject,  and  was  at  once  struck  with  the  totally  different  aspect  of  the  prominences  which  they 
afforded  from  the  appearance  of  the  same  objects  in  the  above-mentioned  photographs  of  previous 
eclipses.  Instead  of  dense,  structureless,  shapeless  patches,  which,  with  uniformly  rounded  out- 
lines, seemed  to  overlap  the  rim  of  the  dark  moon  along  their  entire  extent,  I  found  that  even  the 
most  massive  of  the  protuberances,  the  "  great "  protuberance,  presented  gradations  of  shade, 
exhibiting  thus  interesting  details  of  structure,  and  was  bounded  by  a  very  irregular  outline,  many 
feathery  offshoots  of  gas  being  seen  to  spring  from  the  parent  mass.  The  encroachment  upon  the 
disk  of  the  moon,  also,  instead  of  being  manifest  all  along  the  under  border  of  the  prominences, 
occurred  only  at  isolated  points  where  the  light  from  those  objects  had  been  evidently  very  intense. 
Moreover,  there  were  depicted  many  delicate,  grotesquely-shaped  prominences,  resembling  long 
Hickeriug  flames,  and  of  comparatively  feeble  intensity,  whose  contorted  and  fantastic  outlines 
were  beautifully  defined,  and  exhibited  not  a  trace  of  the  patchy,  beaded  appearance  referred  to, 
nor  the  slightest  indication  of  encroachment  upon  the  limb  of  the  dark  moon. 

From  the  evidence  thus  afforded  by  my  negatives,  which,  be  it  remembered,  were  under- 
exposed,  I  was  at  once  convinced  that  the  peculiar  appearance  of  the  protuberances  in  the  pictures 
of  De  La  Rue  and  Vogel  was  entirely  a  photograph  ic  effect  due  to  excessive  over-exposure  of  the 
plates,  combined  with  want  of  perfectly  sharp  photographic  definition  in  the  telescope.  Now,  it  is 
a  familiar  fact  with  practical  photographers,  or  with  those  who  are  accustomed  to  study  photo- 
graphic effects  critically,  that  the  image  of  a  brilliantly  illuminated  white  object  entering  into  any 
ordinary  view  or  portrait,  where,  of  course,  it  is  over-timed  in  exposure,  is  always  slightly  larger 
upon  the  negative  than  it  should  be,  lacks  the  sharp  outline  of  the  original,  and  has  all  angles  and 
irregular  surfaces  unnaturally  rounded.  Thus,  a  white  dress  in  the  sunlight,  a  flash  of  light  from  a 
diamond,  a  crack  in  a  board  projected  against  a  bright  sky,  are  all  exaggerated  in  size,  and  blunted 
in  outline  in  a  photograph.  There  is,  in  other  words,  in  the  case  of  very  bright  objects  a  photo- 
graphic irradiation  upon  the  sensitive  plate,  precisely  analogous,  though  much  less  in  extent,  to  the 
phenomenon  of  irradiation  in  the  eye.  In  the  same  way  as  a  portion  of  the  retina,  though  itself 
receiving  no  rays,  will  yet  convey  the  perception  of  light  if  the  part  immediately  adjacent  be  very 
strongly  impressed,  so  the  sensitive  iodide  and  bromide  of  silver  in  the  collodion  film  directly 
adjoining  a  portion  that  has  been  subjected  to  a  prolonged  exposure  to  a  brilliant  light,  will  itself 
take  up  the  action,  although  iu  reality  receiving  no  part  of  the  optical  image  of  the  bright  object, 
and  be  capable  under  the  developer  of  attracting  to  itself  the  falling  silver.* 

Though  convinced,  as  previously  stated,  that  herein  was  the  true  explanation  of  the  phenomena 
under  discussion,  yet  to  put  the  existence  of  this  not  generally  recognized  fact  of  "  photographic 
irradiation"  beyond  a  doubt,  and  at  the  same  time  to  show  that  it  will  produce  precisely  those 
curious  effects  observable  in  over-exposed  totality  negatives,  I  made  upon  my  return  to  Washing- 

*  Since  writing  the  above  I  have  been  informed  by  Mr.  Le  Merle,  who,  in  the  course  of  his  photographic  experience, 
has  worked  with  dry  plates,  that  this  action  occurs  with  them  to  a  much  less  extent. 


150  REPORT   OF   DR.    CURTIS. 

ton  some  photographic  experiments  with  an  artificial  total"  eclipse,  devised  so  as  to  reproduce 
exactly  the  optical  conditions  of  the  genuine  phenomenon.  The  contrivance  was  as  follows :  In  a 
piece  of  ordinary  writing  paper  a  few  irregular  holes  were  cut  around  the  circumference  of  a  small 
circle.  A  disk  of  black  paper  of  about  the  same  size  as  this  circle  was  then  pasted  upon  the  writing 
paper  over  it,  so  that  the  cut-out  spaces  should  in  every  instance  seem  to  project  directly  from  the 
edge  of  the  black  disk,  in  the  same  way  as  the  solar  prominences  appear  to  rise  directly  from  the 
moon's  limb  in  a  total  eclipse.  The  scrap  of  writing  paper  so  arranged  was  then  pasted  over  tin- 
disk  of  sunlit  ground  glass  mentioned  in  the  description  of  the  artificial  partial  eclipse  experiment- 
There  were  thus  a  moon,  represented  by  the  disk  of  black  paper;  bright  prominences,  produced  by 
the  intense  light  from  the  ground  glass  passing  unobstructed  through  the  holes  in  the  writing  paper 
and  appearing,  of  course,  as  in  a  genuine  eclipse,  contiguous  to  the  "  moon's"  limb ;  and,  finally,  a 
.corona,  consisting  of  the  feeble  light  that  filtered  through  the  tissue  of  the  white  paper  upon  which 
the  black  disk  was  pasted.  This  little  "  eclipse"  was  then  photographed  with  the  Dallmeyer  triplet, 
an  excessive  exposure  of  several  seconds  being  given  the  negative.  The  plate  was  developed  with  a 
weak  developer,  that  the  action  might  be  slow  and  carefully  watched.  At  first,  of  course,  up  came 
the  mock  prominences  alone,  the  edges  being  clear  and  sharp;  but  as  the  action  of  the  developer 
continued  and  the  little  patches  grew  densely  black,  it  was  apparent  even  to  the  naked  eye  that  the 
deposit  of  silver  was  overstepping  the  limits  of  the  true  optical  image  of  the  prominences,  and  that 
the  edges  were  becoming  blurred  and  the  corners  rounded.  Finally,  the  faint  "  corona"  flashed  out, 
defining  sharply  the  true  position  of  the  edge  of  the  artificial  moon,  and  it  was  then  found  that  in 
all  cases  the  images  of  the  "prominences"  overlapped  the  edge  of  the  ';  moon"  along  their  whole 
extent,  precisely  as  in  an  over-exposed  negative  of  a  real  total  eclipse.  A  second  negative  was 
then  taken  with  double  the  exposure  of  the  first,  and  all  these  effects  occurred  again,  even  more 
strongly  marked  than  before,  the  under  edge  of  the  shorter  prominences  becoming  now  convex 
instead  of  concave  and  bulging  far  into  the  lunar  disk.  Nothing  could  be  more  striking  than  the 
exact  resemblance  of  these  mock  prominences  to  the  beaded  and  sausage-like  appearance  which  the 
real  protuberances  assume  in  an  over-exposed  negative  of  totality. 

Were  any  further  proof  necessary  that  these  appearances  are  purely  photographic  effects,  it  can  be 
found  by  comparing  with  my  pictures  photographs  of  the  same  eclipse  taken  by  other  parties  where 
a  relatively  longer  exposure  was  given.  Such  a  comparison  will  show  that  in  the  latter  pictures 
the  rounding  and  blurring  of  the  edges  of  the  prominences  and  their  encroachment  upon  the  lunar 
disk,  occur  strongly  marked  in  cases  where  the  same  prominences  in  my  own  show  not  the  slightest 
trace  of  these  appearances. 

Now,  that  the  blurring  and  rounding  upon  the  over-exposed  genuine  eclipse  pictures  are  some- 
what greater  than  on  the  artificial  plates  described,  is  unquestionable,  but  it  is  probable  that  in  the 
former  case  some  of  the  effect  must  be  attributed  to  want  of  perfect  photographic  definition  in  the 
telescopes,  the  instruments  used  being  ordinary  achromatic  refractors,  employed  during  totality  with 
tliefull  aperture  of  the  object-glass.  And  since  it  is  likely  that  telescopes  of  this  kind  will  often  have 
to  be  used  for  eclipse  photography,  it  is  important  to  appreciate  fully  the  fatal  effects  of  over-exposure 
upon  the  impression  of  the  prominences  produced  by  the  combined  action  described,  and  to  know 
therefore  that  these  effects  may  not  be  merely  confined  to  a  slight  blurring  and  enlargement  of  the 
photographic  image  of  those  bodies,  but-  may  extend  so  far  as  to  totally  obliterate  all  detail  of 
structure  and  to  render  the  true  outlines  and  characteristic  features  of  the  protuberances  wholly 
unrecognizable. 

Having  thus  reviewed  the  photographs  both  of  the  total  and  partial  phases,  we  may  sum  up 
their  teachings  in  solar  and  lunar  physics  as  follows : 

First.  They  prove  that  the  corona  cannot  belong  to  the  moon,  by  showing  that  it  was  pro- 
gressively eclipsed  by  the  latter  body  in  its  transit  over  the  solar  disk. 

Second.  They  render  it  almost  equally  certain  that  the  corona  does  belong  to  the  sun,  by  exhib- 
iting a  marked  relationship  between  corona  and  protuberances,  and  showing  what  would  a  priori 
be  expected  in  an  extensive  solar  atmosphere,  that  the  corona,  at  the  time  of  the  eclipse  at  least, 
was  comparatively  deficient  in  the  neighborhood  of  the  solar  poles. 

Third.  Considering  the  corona  as  necessarily  a  gaseous  atmosphere,  they  tend  to  confirm  the 
deductions  from  theory  that  the  gas  of  its  composition  must  be  of  exceedingly  low  specific  gravity, 


1869.  151 

and  in  a  state  of  extraordinary  rarefaction,  by  showing  that  the  underlying  red  prominences  on  the 
occasion  of  the  eclipse  exhibited  traces  of  being  acted  upon  by  atmospheric  currents  only  at  one 
spot,  where,  from  the  character  of  the  supposed  current,  the  interpretation  that  this  was  a  local 
eddy,  originating  in  the  chromospheric  matter  itself,  is  as  probable  as  the  aswunption  that  it  was  a 
whirlwind  of  the  corona. 

Fourth.  They  show  that  the  protuberances  are,  certainly  in  the  great  majority  of  instances,  if 
not  invariably,  produced  by  an  upheaving  or  ejecting  force  operating  from  within  or  beneath  the 
envelope  of  the  chromosphere. 

Fifth.  They  exhibit  phenomena  of  which  one  interpretation  may  be  that  the  down-rush  of 
cooled  gas  following  an  unusually  tumultuous  and  extensive  upheaving  of  the  matter  of  the  chromo- 
sphere may  take  the  form  of  an  eddy  or  cyclone  of  unprecedentedly  vast  dimensions. 

Sixth.  They  fail  to  show  any  marked  connection  between  sun-spots  and  protuberances;  one 
stm-spot  only  of  those  visible  on  days  preceding  and  following  the  eclipse  being  even  in  proximity 
to  any  of  the  prominences  seen  during  the  total  obscuration. 

Seventh.  Their  evidence  on  the  question  of  whether  there  was  any  appreciable  motion  to  the 
protuberances  during  the  duration  of  totality  at  Des  Moines  is,  so  far  as  it  goes,  opposed  to  the 
assumption  of  any  such  actual  motion. 

Eighth.  The  evidence  they  aftbrd  that  the  corona  cannot  belong  to  the  moon,  taken  in  con- 
junction with  the  experimental  proof  adduced  that  the  glow  of  light  bordering  the  moon's  limb  as 
projected  upon  the  sun  during  the  partial  phase  is  purely  an  effect  of  diffraction,  and  that  the 
encroachment  of  the  protuberances  upon  the  lunar  disk  in  the  photographs  of  totality  is  a  pbe- 
.  nomenon  of  the  dark-room  alone,  shows  that  none  of  the  varied  phenomena  of  a  solar  eclipse  can  be 
assumed  to  afford  the  least  evidence  of  the  existence  of  an  appreciable  atmosphere  to  the  moon. 

VII.— CONCLUDING  SUGGESTIONS. 

Since  total  eclipses  occur  so  seldom  in  any  given  country  that  it  rarely  falls  to  the  lot  of  a  single 
individual  to  observe  more  than  one  or  two,  the  practical  lessons  as  to  methods  of  observation 
taught  by  the  experience  of  each  eclipse  assume  considerable  importance.  Especially  is  this  the 
case  with  respect  to  photographic  observations,  both  because,  in  general,  photography  more  than 
almost  any  other  art  depends  for  success  upon  the  absolute  perfectness  of  each  and  every  step  in 
the  numerous  operations  required  in  its  practice,  and  because,  as  will  be  the  case  until  the  use  of 
the  art  shall  be  generally  adopted  at  observatories,  the  attempt  to  apply  it  off-hand  to  record  the 
varied  phenomena  of  an  eclipse  must  necessarily  be  made  under  the  very  great  disadvantage  of  the 
work  having  to  be  the  joint  labor  of  an  astronomer  ignorant  of  photography,  and  a  photographer 
equally  unlearned  in  astronomy.  For  photography  can  never  be  learned  by  rote,  nor  practiced  by 
rule:  it  is  an  art  that  requires  in  practice  special  management  and  adaptation  to  suit  the  peculiar 
features  of  the  different  objects  it  is  called  upon  to  picture.  Its  best  resources  can  thus  only  be 
fully  brought  out  for  any  special  work  when  the  operators  are  as  thoroughly  conversant  with  the 
peculiar  nature  and  characteristics  of  the  objects  to  be  photographed,  and  the  photographic  capa- 
bilities and  actual  manipulation  of  the  optical  instrument  to  be  used,  as  with  the  more  familiar 
operations  of  the  dark-room.  In  order  to  contribute,  therefore,  to  this  desirable  general  informa- 
tion on  the  subject  of  the  various  requirements  of  eclipse  photography,  all  the  practical  hints  sug- 
gested by  our  late  experience  will  be  given  in  detail,  unimportant  and  frivolous  though  many  may 
seem  to  the  unprofessional  reader. 

With  respect  first  to  the  telescope:  if  a  refractor  is  used  it  is  almost  needless  to  refer  to  the  im- 
mense advantage  that  would  be  gained  were  the  optical  portion  specially  constructed  for  photography 
both  in  the  matter  of  having  the  lenses  corrected  for  violet  instead  of  mean  white  light,  and  also 
of  having  the  "secondary  magnifier"  constructed  so  as  to  insure  a  flatter  field  than  is  given  by  an 
ordinary  Huyghenian  eye-piece.  As  to  whether  to  use  any  such  magnifier  or  to  receive  the  focal 
image  of  the  object-glass  directly  upon  the  sensitive  plate,  the  arguments  in  favor  of  the  former 
plan  are  given  on  page  124,  but  it  may  be  well  here,  on  account  of  the  general  misapprehension 
of  the  subject  by  such  as  are  not  practical  photographers,  to  say  a  word  on  the  matter  of  photo- 
graphic enlargements.  Now  it  might  appear  to  many  at  first  sight  far  the  better  way  during 
totality  to  use  the  focal  image  alone  to  produce  the  negative,  and  trust  to  subsequent  enlargement 


152  REPORT    OF   DR.    CURTIS. 

to  render  visible  the  hidden  detail  of  the  diminutive  picture.  This  plan,  however,  if  the  object  be 
<i  detailed  representation  of  the  red  protuberances,  is  a  fatal  mistake.  In  the  first  place  it  cannot 
be  too  strongly  insisted  upon  that  the  secondary  enlargement  of  an  image  once  impressed  upon  a 
wet  collodion  plate  can  never,  even  under  the  best  circumstances,  rival  a  negative  obtained  by 
receiving  at  once  upon  the  sensitive  plate  an  equally  good  optical  enlargement  of  the  original  image 
formed  directly  in  the  camera;  for  not  only  does  the  size  of  the  grains  of  silver  forming  the  pho- 
tographic image  put  a  definite  limit  to  the  minuteness  of  detail  that  can  be  recorded  by  the  negative, 
but  it  is  a  well-known  law  in  photography  that  even- in  the  best  copies  a  certain  amount  of  the 
details  and  "half-tones"  of  the  original  picture  is  infallibly  lost  in  the  copying  process.  Secondary 
enlargements,  then,  are  at  best  but  poor  substitutes  for  negatives  of  the  same  size  obtained  by  direct 
amplification  in  the  camera,  where  the  character,  (especially  in  the  matter  ot'JIatncsx,)  the  dimensions, 
and  photographic  brilliancy  of  the  object  to  be  depicted  render  this  possible.  Moreover  it  must  be 
remembered  that  to  produce  even  moderately  good  enlargements,  such  as  they  are,  the  original 
negative  must  be  unusually  excellent.  The  adjustment  of  the  focus  must  be  absolutely  accurate, 
the  length  of  exposure  just  right,  and  the  chemicals  exactly  suited  to  the  character  of  the  object  to 
be  photographed,  so  that  even  the  most  brilliant  lights  may  appear  of  very  moderate  density  in  the 
negative.  And  there  must  be  no  chance  flaw  in  the  collodion  film :  any  accidental  speck,  bubble, 
or  microscopic  shred  of  linen  or  cotton  falling  on  the  plate  from  the  air  might,  from  the  smallness 
of  the  image,  totally  obliterate  some  really  large  and  important  object.  Now  where  there  is  oppor- 
tunity for  repeated  experiments,  as  in  lunar  or  planetary  photography,  trial  after  trial  can  be  made 
until  a  perfect  negative  fit  for  enlargement  is  obtained;  but  during  the  total  phase  of  an  eclipse, 
when  all  has  to  be  staked  upon  half  a  dozen  plates  at  most,  and  when  the  length  of  exposure  even 
for  them  is  necessarily  to  a  great  extent  a  matter  of  conjecture,  the  chances  of  securing  a  negative 
sufficiently  good  to  bear  enlargement  well  are  very  few  indeed.  From  these  considerations,  therefore, 
and  in  view  of  the  fact  now  abundantly  proven  that  the  light -of  the  solar  prominences  exerts  suffi- 
cient chemical  power  to  enable  these  bodies  to  be  photographed  of  a  large  size  at  once,  the  plan  of 
using  the  focal  image  alone  for  their  representation  should  in  my  opinion  be  wholly  abandoned. 
Indeed  I  consider  the  indications  to  be  to  photograph  the  protuberances  on  even  a  larger  scale  than 
that  used  by  me,  with  a  view  of  bringing  out  finer  details  of  their  structure.  But  to  do  this  satis- 
factorily the  optical  part  of  the  telescope  should  be  corrected,  chromatically,  for  violet  light,  though, 
from  the  peculiar  character  of  the  image  to  be  depicted,  no  special  trouble  need  be  taken  to  secure 
flatness  of  field;  for  the  protuberances,  it  will  be  remembered,  form  a  comparatively  narrow  ring  only, 
the  area  which  they  inclose — the  moon's  disk — being  an  absolute  blank.  If  the  focus  is  adjusted  for 
this  ring,  therefore,  and  the  photographic  definition  of  the  instrument  is  good,  a  beautiful  picture, 
of  the  prominences  of  large  size  might  be  obtained  with  a  telescope  which  under  the  same  circum- 
stances would  yield  nothing  but  a  blurred,  worthless  photograph  of  an  object  having  any  great 
extent  of  surface,  such  as  the  disk  of  the  sun  or  full  moon. 

For  the  delineation  of  the  corona,  the  results  obtained  by  Mr.  Whipple  prove  that  the  use  of 
the  focal  image  alone  is  the  only  means  by  which  a  picture  of  that  phenomenon  to  its  full  extent 
can  be  obtained  during  the  short  duration  of  totality.  And  since  the  object  to  be  represented  in 
this  case  is  a  mere  uniform  glow  of  light,  without  any  detail,  the  arguments  used  above  against  this 
method  of  photographing  as  a  means  of  showing  the  solar  protuberances  do  not  apply  here. 

The  flexure  of  the  tube  of  the  telescope  was  a  thing  that  gave  me  a  great  deal  of  annoyance,  and 
one  that  it  seems  to  me  could  be  in  great  part  obviated.  In  the  instrument  used,  if  the  finder  was 
adjusted  so  that  its  axis  was  parallel  with  that  of  the  main  tube  when  the  latter  was  standing 
vertical,  this  parallelism  no  longer  held  good  if  the  telescope  was  swung  horizontal.  During  the 
progress  of  the  eclipse,  therefore,  the  negatives  had  to  be  watched  with  great  care  to  detect  the 
commencement  of  the  inevitable  shifting  of  the  image  from  the  center  of  the  plate,  and  when  this 
was  found  to  occur,  it  was  necessary  to  suspend  the  exposure  of  plates  until  the  finder  could  be 
readjusted.  In  view  of  this  annoyance,  therefore,  it  would  be  well  to  see  that  the  tube  of  an  equa- 
torial intended  for  eclipse  photography  possess  sufficient  rigidity  not  to  bend  to  any  appreciable 
amount,  if,  as  was  the  case  in  August  last,  the  eclipse  is  to  extend  over  an  interval  during  which 
the  sun  is  rapidly  changing  its  altitude. 

My  plan  of  using  a  trigger  to  release  the  slotted  plate  making  the  instantaneous  exposures  for 


OBSERVATIONS   OF   THE    ECLIPSE    OF   AUGUST   7,    ]869.  153 

tbe  partial  phases,  I  cannot  but  regard  as  a  vast  improvement  over  De  La  Eue's  method  of  having 
the  plate  held  by  a  loop  of  thread,  which  is  burnt  off  by  a  lighted  taper  when  it  is  desired  to  make 
the.  exposure.  That  the  trigger  arrangement  is  quicker  to  set  and  less  troublesome  to  work  with, 
are  perhaps  minor  advantages,  but  that  its  use  admits  of  so  much  greater  accuracy  in  the  timing  of 
the  exposures  is  certainly  a  very  important  consideration.  Indeed,  the  method  I  employed  left 
nothing  to  be  desired  in  the  matter  of  accuracy  in  noting  the  exact  instant  of  exposure.  My  plan 
was,  with  eye  and  ear  upon  the  chronometer,  and  thumb  resting  lightly  against  the  under  surface 
of  the  projecting  portion  of  the  wooden  slider  carrying  the  apparatus  for  the  exposures,  to  tap 
gently  on  the  trigger  with  my  forefinger  synchronously  with  the  chronometer  beats  for  several 
seconds  before  exposing,  so  as  to  get  the  rhythm  of  the  time-piece  Avell  fixed  in  my  mind,  and  theii 
at  a  predetermined  even  second,  by  a  slight  increase  in  the  strength  of  the  tap  upon  the  trigger,  to 
release  the  slotted  plate  and  effect  the  exposure.  And  such  was  the  accuracy  obtainable  by  this 
method  that  my  ear,  though  delicate  enough  to  readily  appreciate  the  interval,  minute  as  it  was, 
between  the  click  of  the  trigger  itself  and  the  click  of  the  slotted  plate  striking  home  at  the  end  of 
its  short  course,  was  yet  unable  to  detect  the  slightest  want  of  synchronism  between  the  click  of  the 
trigger  and  the  beat  of  the  chronometer.  The  only  possible  argument  against  the  use  of  the  trigger, 
that  it  involves  touching  the  telescope  and  so  risks  jarring  the  same,  is  entirely  specious,  for  the 
exposure,  being  practically  instantaneous,  is  necessarily  of  shorter  duration  than  the  quickest  jar 
that  can  be  communicated  to  the  instrument.  It  is,  therefore,  really  impossible  to  produce  any 
blurring  or  doubling  of  the  photographic  image  even  by  quite  rough  handling  of  the  trigger,  a 
fact  that  I  took  care  to  prove  by  actual  trial. 

This  method  of  timing  the  exposures  I  therefore  consider  as  far  the  best  that  can  be  adopted. 
The  employment  of  a  chronograph  was  at  one  time  thought  of,  but  a  very  little  reflection  showed 
that  such  an  instrument  would,  under  the  circumstances,  be  worse  than  useless ;  for  to  have  even 
a  theoretical  advantage  over  the  method  of  timing  described  above,  it  would  be  necessary  to  have 
the  seconds  registered  automatically,  a  requirement  that,  to  be  carried  out  in  the  field,  would  involve 
the  construction  and  care  of  special  and  troublesome  apparatus.  And  even  then  the  advantage  of 
the  chronograph  would  be  more  specious  than  real,  for  in  the  method  of  springing  a  trigger 
synchronously  with  a  chronometer  beat,  the  probable  error  in  timing  the  tap  is  actually  less  than 
the  probable  error  of  the  correction  of  the  chronometer,  whose  reading  must  in  any  method  serve 
as  the  basis  for  calculating  the  actual  instant  of  exposure.  And  icithout  an  automatic  registration 
of  the  seconds,  the  use  of  a  chronograph  would  evidently  be  only  a  clumsy,  troublesome,  and  round- 
about way  of  doing  precisely  what  is  effected  by  my  simple  plan  ;  that  is,  instead  of  making  the 
exposure  directly  by  tapping  a  trigger  synchronously  with  the  beat  of  a  chronometer,  the  chrono- 
graph would  require  that  the  seconds  should  be  registered  on  the  instrument  in  precisely  this  way 
by  one  operator,  while  the  exposure  of  the  plate,  made  by  another  operator,  recorded  itself.  This 
chronographic  method  of  timing  would  thus  depend,  after  all,  for  its  exactness  upon  the  accuracy 
with  which  a  tap  can  be  made  with  the  finger  synchronous  with  the  beat  of  a  chronometer.  It  is 
therefore  infinitely  the  simpler  and  better  plan  to  have  this  tap  make  the  exposure  itself,  and  thus 
avoid  both  the  disadvantage  of  the  transportation  and  care  of  an  additional  and  complicated 
piece  of  apparatus  that  is  extremely  liable  to  get  out  of  order,  and  the  very  serious  drawback  of 
the  necessity  of  an  additional  trained  operator  to  attend  exclusively  to  the  marking  of  the  seconds 
by  the  face  of  the  chronometer. 

In  the  construction  of  the  camera  -box  for  my  telescope  a  mistake  was  committed  that  could 
not  be  foreseen  at  the  time,  but  which,  having  proved  a  source  of  annoyance  on  the  day  of  the  eclipse 
by  reason  of  the  hazy  sky,  should  in  future  be  avoided.  This  was  that  the  wooden  slider  carrying 
the  apparatus  for  the  exposures  was  placed  too  far  from  the  eye-piece.  The  effect  of  this  position 
of  the  slider  was  that  instead  of  ordinarily  using,  as  I  had  anticipated,  the  slit  in  the  instantaneous 
plate  about  one-twentieth  of  an  inch  in  width,  I  found  that  for  the  sun  at  the  altitude  it  would 
occupy  during  the  eclipse,  the  whole  width  of  the  slot— half  an  inch— which  had  been  provided  to 
meet  the  emergency  of  unfavorable  weather,  was  necessary  even  with  a  clear  sky,  if  the  usual  two- 
inch  diaphragm  cap  was  used  over  the  object-glass.  Still,  from  the  uniform  clear  atmosphere  that 
prevailed  at  Des  Moiues.  I  anticipated  no  trouble  from  this  source,  not  appreciating  how  very  much 
a  ha/.e  would  cut  down  the  chemical  intensity  of  the  sunlight,  and  therefore  imagining  that  a  three 
20* 


154  REPORT    OF   DR.    CURTIS. 

aud  four  incli  diaphragm  cap,  by  using  which  four  times  the  usual  amount  of  light  could  be  obtained, 
afforded  an  ample  resource  against  the  contingency  of  bad  weather.  This  calculation,  however, 
experience  showed  to  be  a  mistake;  and  thus,  when  the  haze  on  the  critical  day  reduced  the  sun's 
actinic  force,  as  the  eclipse  advanced  and  the  sun  sank  lower  in  the  west,  to  a  tenth  and  a  twentieth 
part  only  of  the  usual  amount,  there  was  no  means  of  allowing  in  the  exposures  for  this  excessive 
diminution  in  the  chemical  power  of  the  light,  but  by  the  very  objectionable  method  of  using  the 
full  aperture  of  the  object-glass ;  objectionable,  because,  as  previously  mentioned,  the  photographic 
definition  of  the  telescope  fell  off  very  considerably  in  sharpness  when  more  than  three  or  four 
inches  aperture  was  allowed  to  the  object-glass.  Since,  therefore,  experience  shows  that  the  sun 
can  be  photographed  through  a  haze  that  will  diminish  its  actinic  force  to  a  small  fraction  of  that 
exhibited  when  the  sky  is  clear,  it  is  important  to  see  that  the  arrangement  of  the  instantaneous 
plate  shall  allow  of  an  increase  of  exposure  to  thirty  or  forty  limes  the  amount  found  necessary 
under  the  circumstances  of  a  clear  sky. 

Another  point  in  the  arrangement  of  the  telescope  from  which  an  unexpected,  and,  in  this 
case,  very  serious  'difficulty  was  experienced  was  the  plan  I  had  adopted  for  viewing  the  image 
from  the  finder  by  allowing  it  to  fall  upon  a  screen  of  white  cardboard.  This  plan,  which  I  had  con- 
sidered the  best  that  could  be  adopted,  because  it  allowed  the  operator  at  the  telescope  to  see  the 
image  from  the  finder  while  handling  the  screws  that  adjusted  the  instrument  for  right  ascension 
and  declination,  should  yet  neA*er  be  trusted  again  for  use  during  totality,  my  experience  having 
shown  that  the  image  of  the  corona  may  readily  be  rendered  so  faint  by  the  passage  of  its  rays 
through  a  hazy  atmosphere  as  to  be  totally  invisible  when  viewed  in  this  way.  In  attempting  to 
improve  upon  this  plan,  however,  the  idea  of  having  the  image  from  the  finder  visible  to  the 
operator  who  adjusts  the  telescope  should  still  be  carried  out;  since  it  is  impossible  to  adjust 
rapidly  where  one  person  observes  the  image  and  another  handles  the  screws.  I  would  therefore 
suggest  that  the  finder  be  mounted  well  up  on  the  tube  of  the  telescope,  and  the  image  received 
upon  a  screen  of  ground  glass,  which  shall  then  be  in  such  a  position  that  the  operator  can  view 
the  image  by  looking  through  and  not  tipon  the  screen,  when  standing  so  as  to  command  the  adjust- 
ing screws  of  the  telescope.  And  care  should  be  taken  that  the  lantern  -to  light  the  face  of  the 
chronometer  during  totality  shall  not  shine  upon  this  screen.  To  provide  against  the  excessive 
brilliancy  of  the  image  of  the  sun  itself  during  the  partial  phases,  colored  glasses  would  have  to 
be  interposed  somewhere  in  the  path  of  the  solar  ray ;  or,  better  still,  perhaps,  a  flap  of  paper  sub- 
stituted for  the  ground  glass,  through  which  the  daz/ling  image  of  the  sun  would  not  appear  too 
bright. 

In  the  important  matter  of  the  proper  length  of  exposure  to  be  given  the  plates  during  totality 
for  the  purpose  of  showing  the  detail  of  the  red  protuberances,  it  is  greatly  to  be  regretted  that 
though  my  negatives  are  so  satisfactory  in  this  respect,  yet  on  account  of  the  exceptional  condition 
of  the  atmosphere  through  which  they  were  taken,  the  exposures  actually  given  cannot  be  relied 
upon  as  a  basis  for  calculation  in  the  future.  For  the  sake,  however,  of  an  approximate  idea  upon 
the  subject,  the  following  analysis  of  the  exposures  is  given  for  what  it  is  worth.  In  the  first  place 
it  must  be  remembered  that  the  negatives,  despite  their  present  beautiful  appearance,  were  really 
considerably  under-exposed,  the  impression  of  the  faint  flame-like  prominences,  and  of  the  corona, 
being  only  brought  out  by  a  dangerous  forcing  of  the  development ;  that  operation  having  been 
pushed,  as  the  plates  show,  to  the  very  verge  of  fogging.  Mr.  Le  Merle,  who  managed  the  devel- 
opment, estimated  at  the  time,  and  still  maintains,  that  the,  proper  exposure  would  have  been  twice 
that  actually  given ;  and  it  is  probable  he  is  right,  for  with  a  fuller  exposure  and  a  quick  develop- 
ment the  contrast  between  the  intensity  of  the  massive  protuberances  and  that  of  the  fainter  and 
more  delicate  forms  would  not  have  been  so  violent.  Starting,  then,  with  double  the  exposure 
actually  given  the  first  totality  negative  as  the  proper  time  it  should  have  had  under  the  circum- 
stances— that  is,  two  minutes  and  twelve  seconds — we  know,  from  the  aperture  of  the  object-glass 
used  in  photographing  the  sun  during  the  partial  phase  immediately  before  totality,  that  the  effect 
of  the  haze  at  that  time  was  to  require  an  increase  of  all  exposures  to  an  amount  at  the  very  least 
ten  times  as  great  as  the  proper  allowance  for  a  fair  day.  But  from  the  fact  that  the  partial  phase 
negatives,  even  with  the  exposure  given,  are  thin  and  weak,  it  is  probable  that  the  absorptive  action 
of  the  haze  should  be  taken  as  considerably  greater,  even  double,  the  above  estimate.  We  thus 


OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST    7,    1869.  155 

obtain  for  the  exposure  that  the  totality  plates  should  have  received,  had  the  sky  been  clear,  a 
range  of  from  six  and  a  half  to  thirteen  seconds,  the  first  number  probably  being  nearest  the  truth. 
These  figures,  however,  it  is  all-important  to  remember,  are  correct  only  for  an  eclipse  occurring  at 
the  same  time  of  year,  and  hour  of  day,  as  that  of  last  August ;  for  a  station  agreeing  pretty  closely 
in  latitude  and  climate  with  the  city  of  Des  Moines ;  for  a  telescope  corresponding  in  dimension 
and  optical  arrangement  with  the  Annapolis  equatorial ;  for  a  photographic  image  of  the  same  size 
as  that  borne  upon  my  negatives ;  and  last,  but  not  least,  for  the  same  bath  and  collodion  as  those 
used  by  Mr.  Ward  in  the  dark-room  of  our  observatory. 

Now,  in  view  of  the  great  number  of  considerations  thus  detailed  as  bearing  upon  the  question 
of  length  of  exposure,  it  is  very  desirable  to  determine  accurately  what  Do  La  Eue  attempted  to 
estimate,  namely,  the  comparative  photographic  intensity  of  the  light  from  the  solar  prominences 
and  full  moon.  For  when  this  is  accomplished,  the  would-be  eclipse  photographer  can  calculate 
very  closely  the  proper  totality  exposure  for  a  special  eclipse,  station,  telescope,  and  chemicals,  by 
transporting  telescope  and  chemicals  to  the  station  in  time  to  photograph  on  the  spot  the  last  full 
moon  before  the  eclipse,  being  careful  to  take  the  moon  at  as  nearly  as  possible* the  same  altitude 
that  the  sun  is  to  occupy  during  totality. 

On  this  question  of  the  relative  chemical  intensity  of  these  two  kinds  of  light,  it  is  again 
unfortunate  that  our  experience  cannot  speak  decisively,  since  the  proper  exposure  for  us,  both  for 
the  prominences  during  the  eclipse  and  for  the  full  moon,  is  a  matter  of  so  much  uncertainty.  But 
such  as  it  is,  the  result  is  as  follows:  The  probable  correct  exposure  for  the  prominences,  in  the  case 
of  a  clear  sky,  we  have  found  to  be  six  and  a  half  seconds;  and  the  probable  correct  exposure  for 
the  full  moon  at  the  same  altitude  my  preliminary  experiments  showed  to  be  twenty  minutes. 
These  figures  would  give  as  the  relative  chemical  intensity  of  the  light  of  the  solar  prominences 
and  the  full  moon,  the  ratio  of  184  to  1,  a  proportion  almost  identical  with  that  deduced  by  De  La 
Eue  from  his  experiments.  The  corroborative  evidence  thus  adduced  points  strongly  to  the 
accuracy  of  that  astronomer's  estimate,  and  it  is  therefore  safe  to  say  that  the  plan  of  experiment- 
ing upon  the  full  moon,  and  then  calculating  the  totality  exposure  according  to  the  above  ratio,  is 
probably  the  most  reliable  way  of  attacking  the  question. 

But  still,  the  first  exposure  during  totality  must  .be  to  a  great  degree  conjectural ;  and  the 
timing  of  the  subsequent  plates  must  be  regulated  by  the  result  of  development  of  the  first.  The 
operator  at  the  developing  tank  has  thus  the  vitally-important  duty  to  perform  of  estimating 
quickly,  but  coolly  and  accurately,  from  the  manner  in  which  the  image  "  comes  up,"  what  modi- 
fication should  be  made  in  the  exposure  for  the  succeeding  plates.  It  is  needless  to  say,  therefore, 
that  this  post,  the  most  responsible  of  all  during  totality,  should  be  intrusted  only  to  a  most 
accomplished  photographer,  who  understands  thoroughly  the  nature  of  the  object  pliotographed,  and  the 
exact  effect  which  it  is  desired  to  produce.  And  in  future  this  operator  will  find  a  valuable  auxiliary 
guide  to  a  correct  estimation  of  the  proper  exposure,  in  those  peculiar  eifects  on  the  impression  of 
the  prominences  which  I  have  pointed  out  as  due  to  over-exposure.  (See  page  149.)  That  is,  if  on 
developing  a  totality  negative  the  prominences  come  up  with  their  base  markedly  convex  towards 
the  body  of  the  sun,  there  is  no  necessity  of  waiting  for  the  completion  of  the  development,  and  a 
careful  inspection  of  the  amount  of  detail  obtained ;  but  the  operator  at  the  telescope  may  be  at 
once  notified  that  the  exposure  must  be  reduced.  By  this  means  time  can  be  saved — an  all-important 
consideration  during  the  few  precious  minutes  of  totality. 

As  to  the  proper  exposure  for  the  corona,  my  negatives  of  course  are  silent,  since  this  object  is 
but  very  faintly  impressed  upon  them ;  but  it  may  not  be  amiss  to  state  that  a  most  accurate  basis 
for  calculation  on  this  subject  is  afforded  by  the  splendid  photographs  of  the  corona  already  alluded 
to  as  obtained  by  Mr.  Whipplc,  at  Shelbyville,  Kentucky.  The  best  of  these — which  shows  the 
corona  very  nearly  if  not  quite  as  extensive  and  brilliant  as  it  appeared  to  the  eye — we  learn  was 
exposed  for  forty  seconds ;  the  focal  image  of  a  six-inch  object-glass  being  received  directly  upon 
the  sensitive  plate.  Mr.  Whipple  also  writes  :*  "  The  day  was  splendid ;  not  a  cloud  to  be  seen." 
But  allowance  should  still  be  made  in  a  calculation  upon  this  exposure  for  the  low  altitude  of  the 
sun  at  Shelbyville  at  the  time  of  totality. 

With  respect  to  the  nature  of  the  photographic  chemicals  best  suited  for  negatives  of  the  phe- 

*  Philadelphia  Photographer,  September,  1869,  page  291. 


156  REPORT    OF   DR.    CURTIS. 

noiuena  of  totality,  the  bountiful  results  obtained  by  us  speak  loudly  in  favor  of  the  formula-  em- 
ployed, and  prove  the  correctness  of  our  reasoning  that  for  this  peculiar  subject  a  well-bromized 
collodion  yielding  soft  thin  negatives  full  of  detail,  is  infinitely  superior  to  one  giving  the  brilliant 
dense  negatives  abounding  in  striking  contrasts,  which  so  many  photographers  are  accustomed  to 
use.  It  may  also  be  added  that  since,  as  a  general  rule,  the  difficulty  in  exposing  for  the  solar  prom- 
inences is  not  to  get  a  long  enough,  but  a  sufficiently  short  exposure,  the  supposed  necessity  for  a 
neutral  bath  in  order  to  obtain  the  greatest  possible  sensitiveness,  does  not  exist ;  and  it  is  better, 
therefore,  to  use  the  ordinary  acid  bath  than  incur  the  danger  of  fogging,  which  is  always  to  be 
apprehended  when  the  neutral  silver  solution  is  employed. 

In  the  matter  of  the  arrangement  of  the  dark-room  and  apportionment  of  labor  during  the 
eclipse,  I  can  suggest  no  improvement.  The  trough  of  water  to  hold  the  negative  baths  we  found 
absolutely  indispensable  on  account  of  the  excessive  heat  of  the  dark  room  on  sunny  afternoons. 
Without  the  troughs  the  temperature  of  the  baths  was  found  to  rise  as  high  as  83°  Fahrenheit,  with 
fogging  of  the  plates  as  an  inevitable  result.  The  plan  of  having  the  reservoir  of  water  outside  the 
building — borrowed  from  De  La  Hue — proved  a  great  convenience  in  the  matter  of  keeping  the 
barrel  filled ;  and  the  large  fixiug-trough  and  dumb-waiters  for  passing  the  plateholders  in  and  out 
were  not  only  conveniences,  but  really  did  the  part  of  two  additional  operators.  The  division  of 
labor  among  the  four  of  us  on  the  occasion  of  the  eclipse  itself,  was  so  even  that  the  operations  per- 
formed by  each  took  almost  exactly  the  same  amount  of  time,  so  that  we  were  enabled  to  all  work 
together  and  accomplish  the  greatest  amount  of  work  in  the  shortest  possible  time. 

In  conclusion,  to  serve  as  some  guide  to  future  expeditions  of  this  kind,  I  have  thought  it  well 
to  give  a  list  (see  Schedule  C)  of  the  articles  taken  by  us  as  our  photographic  equipment,  with  the 
remark  that  of  the  extensive  and  somewhat  heterogeneous  assortment  of  materials  and  implements 
there  given,  there,  was  scarcely  a  thing  that  did  not  come  into  play.     The  list  was  made  thus  com 
plete,  in  the  first  place,  because  at  the  time  of  our  starting  on  the  expedition  we  thought  it  likely 
that  we  might  take  our  station  at  Mitchellville  instead  of  Des  Moines;  and  the  former  being  a  very 
small  country  village,  I  considered  it  necessary  to  go  thoroughly  equipped  in  every  particular,  even 
to  the  being  prepared  to  build  the  observatory  with  our  own  hands  and  tools. 
I  am,  General, -very  respectfully,  your  obedient  servant, 

EDWA14D  OUKTIS, 
Assistant  Surgeon  and  Brevet  Major  U.  8.  Army. 

Brevet  Major  General  J.  K.  BARNES, 

Surgeon  General  United  States  Army. 


OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST   7,    1869. 
SCHEDULE  A.—i:«;ii'il  of  .Yr;/(fJi><«. 


157 


Date. 

Designat'u  of  neg- 
ative. 

rr  ^ 

X    •  , 

V   ft 

5* 

pi 

H 

Instant  of  expos- 
ure by  local 
mean  time  p.m. 

Diameter  of  aper- 
ture of  object 
glass  used. 

Widthofslitinin- 
stantau'us  slide 
used. 

Remarks. 

1889. 

/I.     HI.     «. 

/I.  HI.      a. 

in. 

I'H. 

July        26 

A 

11     3  25 

4  46    7.9 

2i 

A 

Chronometer  fast  61'  17m  17s.  1. 

28 

B 

11  14  55 

4  57  37.5 

2| 

ft 

Chronometer  fast  6h  17m  17s.  5. 

29 

C 

8  49  55 

2  32  38.  4 

2 

4 

Chronometer  fast  61'  17m  16s.  6. 

30 

D 

8  52  15 

2  34  59.  1 

2| 

I 

Chronometer  fast  6h  17m  15«.9. 

31 

E 

10  37  30 

4  20  13.5 

3 

A 

Chronometer  fast  6h  17m  16'.  5. 

August     2 

F 

12    G  55 

5  49  38.6 

4 

i 

Chronometer  fast  6h  17m  16s.  4. 

3 

G 

10    1  45 

3  44  29.  5 

2 

i 

Chronometer  fast  6h  17<"  15s.  5. 

4 

H 

7  41  15 

1  23  59.6 

2i 

i 

Chronometer  fast  6h  17™  15".  4. 

7 

I 

8  59  45 

2  42  29.  0 

3 

n 

Iti 

Chrono-jieter  fast  6h  17m  16".  0. 

1 

9  59  57 

3  42  41.  0 

6 

i 

8 

10    0  14 

3  42  58.  0 

6 

1 

3 

10     0  46 

3  43  30.  0 

6 

i 

First  plate  showing  contact. 

4 

10     1     7 

3  43  51.0 

6    . 

4 

5 

10     1  23 

3  44     7.0 

6 

1 

6 

10     1  40 

3  44  24.  0 

6 

i 

7 

10    1  54 

3  44  38.0 

6 

i 

8 

10     (i  15 

3  48  59.  0 

6 

i 

9 

It)    7  15 

3  49  59.  0 

6 

i 

10 

10     8  15 

3  50  59.  0 

6 

* 

11 

10     9  15 

3  51  59.0 

6 

}' 

• 

12 

10  10  15 

3  52  59.  0 

6 

J 

13 

10  11  15 

3  53  59.  0 

6 

4 

14 

10  12  20 

3  55    4.  0 

6 

4 

15 

10  13  20 

3  56    4.0 

6 

4 

16 

10  14  15 

3  56  59.  0 

6 

4 

17 

10  15  15 

3  57  59.  0 

6 

4 

18 

10  16  15 

3  58  59.  0 

6 

i 

19 

10  17  15 

:i  59  59.  0 

6 

4 

20 

10  18  15 

4    0  59.  0 

6 

1 

21 

10  19  15 

4     1  59.0 

6 

4 

22 

10  20  25 

4    3    9.0 

6 

i 

23 

10  21  15 

4    3  59.  0 

6 

4 

24 

10  22  15 

4    4  59.  0 

6 

i 

25 

10  23  15 

4    5  59.  0 

6 

1 

26 

10  24  15 

4    6  59.  0 

6 

i 

27 

10  25  20 

4     8     4.0 

6 

| 

28 
29 

10  26  15 
10  37  20 

4    8  59.  0 
4  10    4.0 

6 
6 

} 
| 

Large  sun-spot  on  southwestern  portion  of  SHU'S 
disk  bisected  by  moon's  limb. 

30 

10  28  15 

4  10  59.  0 

6 

i 

31 

10  29  15 

4  11  59.0 

6 

i 

32 

10  30  15 

4  12  59.  0 

6 

| 

33 

10  31  15 

4  13  59.0 

6 

i 

34 

10  32  15 

4  14  59.0 

6 

i 

35 

10  33  15 

4  15  59.  0 

6 

1 

36 

10  34  15 

4  16  59.  0 

6 

A 

158 


REPORT   OF    DR.    CURTIS. 


SCHEDULE  A.—Scconl  o/Ai#««r<-«— Continued. 


Date. 

tt> 
9 

a 

Is 
I1 

8  3 

Mc 

X      K-. 

<u  & 

=  fe. 

4-   ' 

S                LC 

s  ss 

«       £    i-H 

£ 

Instant  of  expos- 
ure by  local 
mean  time  p.  in. 

Diameter  of  aper- 
ture of  object 
glass  used. 

Width  of  slit  inin- 
stantan'us  slide 
used. 

Remarks. 

1869. 

/I.     JM.     «. 

7l.   Ml.         *. 

in. 

in. 

August    7 

37 

10  35  15 

4  17  59.0 

6 

i 

38 

10  36  15 

4  18  59.  0 

6 

4 

• 

38 

10  37  15 

4  19  59.  0 

6 

i 

40 

10  38  15 

4  20  59.  0 

74 

i 

41 

10  39  15 

4  21  59.0 

74 

i 

42 

10  40  15 

4  22  59.  0 

7f 

i 

43 

10  41  15 

4  23  59.  0 

74 

i 

44 

10  42  15 

4  24  59.0 

7f 

a 

45 

10  43  15 

4  25  59.  0 

74 

4 

46 

10  44  15 

4  26  59.  0 

74 

i 

• 

47 

10  45  15 

4  27  59.  0 

74 

4 

48 

10  46  15 

4  28  59.  0 

7} 

4 

49 

10  47  25 

4  30    9.0 

7f 

4 

50 

10  48  20 

4  31    4.0 

7i 

'4 

51 

10  49  15 

4  31  59.0 

7* 

4 

5-2 

.     .     . 

74 

4 

Trigger  liunj;  tire;  time  not  noted. 

53 

10  51  15 

4  33  59.0 

7f 

i 

54 

10  52  15 

4  34  59.0 

74 

4 

55 

10  53  15 

4  35  59.  0 

74 

4 

56 

10  54  20 

4  37     4.  0 

74 

A 

57 

10  55  15 

4  37  59.  0 

74 

4 

58 

10  56  15 

4  38  59.  0 

7f 

4  • 

59 

10  57  15 

4  39  59.  0 

7f 

n 

60 

10  58  15 

4  40  59.  0 

7* 

| 

61 

10  59  20 

4  42    4.0 

74 

4 

. 

(11     3    4 

4  45  48.  0^) 

03 

to 

to 

7J 



Totality.     Exposed  (K5  seconds. 

111     4  10 

4  46  54.  oj 

fll     4  47 

4  47  31.0^1 

63 

to 

to 

7J 

Totality.     Exposed  45  seconds. 

111     5  32 

4  48  16.  OJ 

64 

11     6     5 

4  48  49.  0 

•       74 

.     i 

<>5 

11     7  20 

4  50    4.  0 

7f 

.     4 

06 

11     8  35 

4  51  19.  0 

74 

4 

67 

11     9  15 

4  51  59.  0 

7f 

4 

68 

11  10  15 

4  52  59.  0 

74 

4 

69 

11  11  15 

4  53  59.  0 

7* 

4 

70 

11  12  20 

4  55    4.  0 

74 

} 

71 

11  13  15 

4  55  59.  0 

74 

} 

72 

11  14  15 

4  56  59.  0 

74 

Y 

73 

11  15  25 

4  58    9.0 

74 

4 

74 

11  16  15 

4  58  59.  0 

74 

i 

, 

75 

11  17  25 

5    0    9.0 

.   7f 

4 

76 

11  18  20 

5    14.0 

74 

4 

[port  inn  of  sun's  disk. 

77 

11  19  35 

5    2  19.  0 

7J 

4 

Reappearance  of  large  sun-spot  on  southwestern 

78 

11  20  15 

5    2  59. 

7J 

4 

Trigger  hung  lire  slightly  ;  timing  not  accurate. 

OBSERVATIONS    OP   THE   ECLIPSE    OF   AUGUST   7,    1869. 


159 


SCHEDULE  A.— Record  of  Xeyatiees— Continued. 


Date. 

if 

a 

?l 

a 

tc 

1 

i! 

^  tC 
a    v 

_i2 
• 

h-H 

a  «—.  -H 

-*3                    ~- 

fl     O     3 
C3    ^     Qj 

a  "  " 

M 

Diarneterof  aper- 
ture of  object 

glass  used. 

AVidthofslitinin- 
stantan'us  slide 
used. 

Remarks. 

1869. 

/I.     III.     S. 

It.  ill.        S. 

i» 

in. 

August     7         79 

11  21  15 

5    3  59.  0 

7} 

i 

80 

11  22  20 

5     5    4.  0 

71 

1 

81 

11  23  15           5    5  59.0 

71 

1 

82 

11  24  15           5    6  59.0             7J 

1 

83 

11  25  15 

5    7  59.0             7f 

4 

84 

11  26  25 

5    9    9.0 

71 

i 

85 

11  27  15 

5    9  59.0 

71 

i 

. 

86 

11  28  25 

5  11     9.0 

71 

| 

87 

11  29  15 

5  11  59.0 

71 

i 

88 

11  30  15 

5  12  59.  0 

71 

4 

89 

11  31  15 

5  13  59.  0 

7J 

i 

90 

11  32  20 

5  15    4.0 

71 

£ 

91 

11  33  15 

5  15  59.0 

71 

4 

• 

92 

11  34  15 

5  16  59.  0 

71 

i 

93 

11  37  15 

5  19  59.  0 

71 

j 

94 

11  38  20 

5  21     4.  0 

71 

4 

95 

11  39  20 

5  22     4.  0 

71 

4 

96 

11  40  15 

5  22  59.  0 

71 

j 

97 

11  41  15 

5  23  59.  0 

•      71 

i 

98 

11  42  15 

5  24  59.  0 

71 

4 

99 

11  43  15 

5  25  59.  0 

7J 

+ 

100 

11  44  15 

5  26  59.  0 

71 

1 

101 

11  45  15 

5  27  59.  0 

71 

I 

102 

11  46  15 

5  28  59.  0 

7* 

i 

103 

11  47  15 

5  29  59.  0 

71 

i 

Fogged  and  spoiled.* 

104 

11  48  15 

5  30  59.0 

71 

i 

105 

11  49  15 

5  31  59.  0 

71 

4 

106 

11  50  40 

5  33  24.  0 

71 

i 

Fogged  and  spoiled.* 

107 

11  51  15 

5  33  59.  0 

7J 

1 

108 

11  52  15 

5  34  59.  0 

71 

4 

109 

11  53  15 

5  35  59.0 

7} 

I 

110 

11  54  20 

5  37    4.  0 

7} 

^ 

111 

11  55  15 

5  37  59.  0 

71 

1 

112 

11  56  15 

5  38  59.  0 

71 

4 

Fogged  and  spoiled.* 

113 

11  57  15 

5  39  59.  0 

7J 

1 
2 

114 

11  58  15 

5  40  59.  0 

71 

4 

Reappearance  of  large  sun-spot  on  eastern  por- 

115 

11  59    0 

5  41  44.0 

7f 

4 

tion  of  sun's  disk. 

116 

12    1  15 

5  43  59.  0 

71 

4 

117 

12    1  28 

5  44  12.  0 

71 

4 

. 

118 

12    1  42 

5  44  26.  0 

71 

4 

119 

12    1  58 

5  44  42.0 

71 

J, 

120 

12    2  17 

5  45    1.  0 

71 

4 

Last  plate  showing  contact. 

121 

12    2  43 

5  45  27.  0 

71 

4 

122 

12    3  16 

5  46    0.  0 

7J 

4 

August     8 

K 

9  34  30 

3  17  13.6 

2 

i 

Chronometer  fast  61'  17™  16M. 

9 

L 

8  K)  :,:, 

1  53  38.4 

2 

4 

Chronometer  fast  6h  17m  16S.C. 

*Fog#iDg  due  to  a  batch  »f  cleaned  plati-slwin^  s«>t  on  a  pad  of  lilottiinj.  (i:t]M-r  that  was  accidentally  damp.    As  soon  as  the  cause  of  the 
difficulty  was  discovered  thin  batch  was  discarded. 


160 


REPORT   OP   DR.    CURTIS. 


SCHEDULE  B. 

Table  showing  the  relative  actinic  force  of  the  sun  at  different  altitudes,  as  determined  by  comparing 
shades  of  blackening  of  photographic  paper  produced  by  exposure  to  direct  sunlight  at  different  times 
of  day  for  a  series  of  definite  intervals  of  time  ranging  from  half  a  second  to  ten  minutes.* 


, 

'       4> 

r—         - 

<"  ji   (•<   a 

<0    <H      <U 

• 

'       — 

c^     a)      • 

°  C    s 

J3     ^     ~" 

~  -  § 

*"  "S  ** 

*  a 

*   d 

PfRjt 

-  •? 

W      •!-» 

o    o  'fl 

X               t-t 

9    A    fi 

"3   = 

"8  ^ 

-   r"  § 

no     *>     S 

111* 

|J 

Date. 

Commencement 
lire.  Local  me 

Greatest  duratioi 
lire  of  shade  n 
comparison. 

Number  of  shade 
by  different 
used  in  the  co: 

Relative  actinic  i 
sunlight  comp 
that  exhibited 
noon  of  each 
standard. 

Altitude  of  the  i 
time  of  comme 
exposure,  give 
nearest  degree. 

Keniarks. 

1869. 

/I.       HI. 

Ml.       8. 

o        ' 

July        27 

12      0 

. 

. 

1.000 

67 

Standard.     Sky  hazy. 

2    45  p.  m. 

1    35 

4 

.105 

49 

Very  hazy  ;  sun  scarcely  cast  a  shadn\v. 

28 

7    54a.m. 

1      0 

6 

.568 

31 

8    54 

1      0 

15 

.786 

42 

10    23 

0     30 

11 

1.333 

58 

12      4p.m. 

- 

1.000 

07 

Standard. 

1     50 

1      0 

18 

1.000 

58 

3      1 

1      0 

18 

1.000 

40 

4     11 

1      0 

15 

.786 

34 

5      6 

0    50 

8 

.480 

23 

0      0 

1     35 

7 

.096 

13 

29 

5    13  a.m. 

10      0 

8 

.035 

2    30 

5    28 

8    20 

9 

.095 

5 

5    43 

3    20 

6 

.145 

7    30 

5    58 

1      0 

5 

.163 

10 

0     16 

0    40 

7 

.263 

15 

6    28 

0    40 

9 

.424 

16 

6    43 

0    25 

7 

.433 

18    30 

6    58 

0    50 

9 

.499 

21 

7     13 

1      0 

10 

.568 

24 

7    28 

0    50 

10 

.636 

27 

7    43 

1      0 

15 

1.000 

30 

7    58 

1      0 

15 

1.000 

33 

8    13 

1      0 

15 

1.000 

35    30 

8    28 

1      0 

15 

1.000 

38 

8    43 

1      0 

15. 

1.000 

41 

9    13 

1      0 

15 

1.000 

46     30 

9    45 

1      0 

15 

1.000 

52    30 

10     16 

1      0 

15 

1.000 

57    30 

11      0 

1      0 

15 

1.000 

03 

12      0 

. 

. 

1.000 

67 

Standard. 

1      3p.m. 

1      0 

15 

1.000 

04 

2      0 

1      0 

15 

1.000 

56    30 

3      0 

1       0 

9 

.732 

46    30 

4      1 

1      0 

10 

.677 

34    30 

4     13 

1      0 

10 

.615 

33 

4    28 

1      0 

9 

.518 

30 

• 

4    43 

1      0 

10 

.493 

27    30 

'  For  an  explanation. of  the  method  by  which  these  observations  \\civ  ni;nlt-.  see  page  130. 


OBSERVATIONS   OP   THE   ECLIPSE    OF   AUGUST   7,    1869. 


161 


SCHEDULE  B.— Continued. 


I 

S  — 

©  S 

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162 


REPOET    OF    DR.    CURTIS. 


SCHEDULE  C. 


List  of  articles  forming  the  equipment  of  the  photographic 


I.  CHEMICALS. 


Ammonia , .  8  ounces. 

Acetic  acid 8  pounds. 

Alcohol,  Atwood's 2  gallons. 

Bichloride  of  mercury 2  ounces. 

Bichromate  of  potassa 3  pounds. 

Bromide  of  cadmium 3  ounces. 

Cyanide  of  potassium 1    pound. 

Caustic  potassa 8  ounces. 

Carbonate  of  soda 1   pound. 

Distilled  water* 5  gallons. 

Ether 3  quarts. 

Hyposulphite  of  soda 15  pounds. 


Iodine 

Iodide  of  ammonium ' 

Iodide  of  cadmium 

Iodide  of  potassium 

Negative  varnish  • 

Nitric  acid 

Nitrate  of  silver  (recrystallized) . 

Paraffine 

Permanganate  of  potassa 

Pyroxyline 

Sulphate  of  iron 

Sulphuric  acid 


12 
4 


1  ounce. 

2  ounces. 
2  ounces. 
4  ounces. 

ounces, 
ounces. 


3  pounds. 
1   pound. 
1    ounce. 

4  ounces. 
4  pounds. 
3  pounds. 


II.  PHOTOGRAPHIC  INSTRUMENTS,  MATERIAL,  AND  APPLIANCES. 


Actinometers. 

Balance  and  weights. 

Bottles,  assorted. 

Beakers. 

Capsule  tongs. 

Chamois  skin. 

Corks,  assorted. 

Corkscrew. 

Cork-squeezer. 

Crocks  for  cleaning  solution  for  plates. 

Dipping-rods. 

Dumb-waiters  for  wall  of  dark-room. 

Dusting-brushes  for  negatives. 

Evaporating  dishes. 

Filtering  paper. 

Filtering  stands. 

Funnels. 


Graduates. 

Ground  glass  for  camera  screens. 

Glass  plates  for  solar  negatives. 

Glass  plates  for  stereoscopic  negatives. 

Hard  rubber  photographic  trays. 

Magnesium  ribbon. 

Mortar  and  pestle. 

Photographic  paper. 

Photographic  ware  baths  for  negatives. 

Precipitating  glasses. 

Betort  stands. 

Backs  for  negatives. 

Spirit  lamps. 

Stereoscopic  camera  and  stand. 

Stereoscopic  and  other  lenses. 

Test  paper. 


Beeswax. 

Black  velvet. 

Candles. 

Candle-sticks. 

Carpenter's  and  other  tools. 

Coal  oil. 

Cardboard. 

Cotton-wool. 

Cotton-flannel. 

Copper  still,  1  gallon  capacity. 

Glue. 

Glue-pot. 

Glazier's  diamond. 

Hinges,  springs,  and  latches,  for  doors. 

Lamps. 

Lamp  oil. 

Lanterns. 

Listing. 

Mathematical  instruments. 

Matches. 

Mucilage. 

Muslin. 

Naphtha  stove  and  naphtha. 

Nails,  screws,  and  tacks,  assorted. 


III.  MISCELLANEOUS. 

Paper — black,  blotting,  tissue,  yellow. 
Photographic  books. 

Pulleys  and  staples  for  hauling  canvas  roof. 
Pins. 

Perforated  tin  for  guarding  delivery  and  waste- 
pipes. 
Rope. 

Eubber  bauds. 
Eubber  cloth. 

Eubber  tubing  for  water  and  waste-pipes. 
Sail-maker's  thread,  needles,  and  palm. 
Sheet  tin. 
Soap. 

Sealing-wax. 
Sponges. 
Spigots. 
Stationery. 
Tent-flies  for  roof. 
Tape. 
Tape-line. 
Towels. 
Twine. 
Wax  tapers. 
Writing  diamond. 


Oil-can  and  machine  oil. 
Buckets  for  carrying  water,  a  wash-tub  to  make  a  sink  of,  and  other  bulky  and  common  articles, 
were  procured  at  Des  Moines. 

*  In  addition  a  small  still  was  taken,  which  was  kept  constantly  in  operation  during  our  stay  at  Des  Moines. 


REPORT 


MR.    J.    HO  I  EH    LANE. 


REPORT   OF   MR.   J.    HOMER   LANE. 


.  WASHINGTON,  D.  C.,  Augwt  28, 1869. 

SIR:  Having  beeu  attached  to  the  party  of  Professor  J.  E.  Hilgard,  of  the  United  States  Coast 
Survey,  for  observing  the  recent  eclipse  of  the  sun,  I  am  directed  by  him,  in  conformity  with  an 
arrangement  approved  by  Professor  Xewcomb,  of  the  United  States  Naval  Observatory,  to  report 
to  you,  in  part,  such  observations  as  I  made  on  that  occasion. 

At  the  request  of  Professor  Hilgard  I  joined  his  party,  and  proceeded  to  the  city  of  Des 
Moines,  in  the  State  of  Iowa,  to  meet  him  and  the  other  members  of  his  party  there.  I  was 
expected  to  note  the  times  of  the  first  and  fourth  contacts  of  the  moon's  limb  with  the  sun's  limb. 
These  observations  were  taken  accordingly,  and  have  been  duly  reported  to  Professor  Hilgard. 
The  times  of  second  and  third  contacts  were  left  to  my  own  discretion,  conditioned  on  their  non- 
interference with  the  phenomena  of  totality.  I  therefore  did  not  attempt  them. 

Beyond  the  observation  of  the  times  of  first  and  fourth  contacts  it  was  understood  that  my 
attentiou  should  be  primarily  given  to  the  corona,  but  the  particular  point  or  points  of  inquiry 
were  left  mostly  to  my  own  discretion.  As  various  physical  considerations  which  have  been  pre- 
sented in  published  papers  of  Professor  Helmholtz  and  Professor  Newcomb,  and  in  a  paper  of  my 
own  not  yet  published,  but  in  part  presented  to  the  National  Academy  at  its  late  session  in  Wash- 
ington, have  left  upon  myself,  as  well  as  both  the  individuals  just  named,  a  strong  impression  of  the 
extreme  difficulty  of  realizing  the  existence  above  the  sun's  photosphere  of  an  atmosphere  in  the 
ordinary  sense  of  that  term,  having  such  a  height  as  fifty  or  a  hundred  thousand  miles,  I  proposed 
to  make  it  the  chief  object  of  my  own  observation  to  watch  for  any  indication  that  could  bear  on 
that  question.  More  particularly  I  charged  myself  with  the  duty  of  watching  for  any  possible 
very  low  atmospheric  limit,  marked  by  anything  like  a  regular  boundary  and  superior  intensity  of 
light  very  near  the  sun's  limb. 

According  to  the  original  intention,  I  was  to  have  used  a  Coast  Survey  reconnoitering  tele- 
scope of  only  three  inches  clear  aperture;  but  after  my  arrival  in  Des  Moiues,  which  was  not  till 
12  or  1  o'clock  of  the  Thursday  night  immediately  preceding  the  eclipse,  Professor  Newcomb,  who, 
on  the  part  of  the  Naval  Observatory,  had  charge  of  the  court-house  square  observatory  in  Des 
Moines,  proposed  to  Professor  Hilgard  that  I  should  observe  with  one  of  the  much  larger  instru- 
ments which  he  had  fitted  up.  One  of  these  remained  unappropriated,  and  was  accordingly 
assigned  to  my  use.  The  object-glass  was  that  of  the  refraction  circle  of  the  United  States  Naval 
Observatory.  Having  beeu  taken  from  its  tube  and  conveyed  to  the  station  at  Des  Moines 
it  was  there  fitted  to  a  temporary  wooden  tube  mounted  in  such  a  manner  as  to  command  the 
sun  during  the  eclipse.  This  glass  has  a  clear  aperture  of  5.9  inches  in  diameter,  and  a  focal 
length  of  about  eight  feet  seven  inches,  according  to  a  rough  measurement  which  I  made  since 
my  return  to  this  city.  The  eye-piece  I  employed,  one  of  a  set  furnished  also  by  the  observatory, 
was  a  positive,  or  Eamsden,  eye-piece,  in  the  field  of  view  of  which  0.2G  inch  is  found  to  sub- 
tend to  the  eye  .an  angle  of  about  13°  36',  which  corresponds  to  a  virtual  or  compound  focal  length 
of  1.1  inches.  The  magnifying  power  of  the  instrument  was,  therefore,  not  far  from  94.  The  tem- 
porary wooden  tube  was  square  in  cross-section,  and  the  eye-piece  was  mounted  on  a  square  piece 
of  board  fitted  to  the  interior  of  the  tube.  The  focal  adjustment  could  be  made  by  sliding  this  piece 
of  board  a  little  to  and  fro  in  the  tube,  and  a  thin  narrow  wooden  wedge  introduced  near  the  upper 
right-hand  corner  of  the  piece  of  board  served  effectually  to  secure  it  in  its  place.  The  square 
wooden  tube  was  mounted  so  as  to  swing  at  its  middle  in  a  wooden  gimbal  constructed  of  four 
pieces  of  stout  plank,  and  this  gimbal  turned  on  a  nearly  horizontal  axis  pointing  not  far  from 


166  KEPORT   OF   MR.    J.    HOMER   LANE. 

north  and  south,  being  supported  by  a  pair  of  heavy  upright  timbers  or  posts,  set  firmly  in  the 
ground.  The  tube  was  well  counterpoised  or  balanced,  and  was  steadied  by  means  of  a  pair  of 
braces  extending  from  the  tube  to  the  posts.  Each  brace  consisted  of  a  long  lath  of  soft  pine  wood. 
The  connection  of  the  lath  to  the  post  was  made  by  a  common  wood  screw,  passed  through  a  hole 
in  the  lath  and  set  into  the  post.  Another  wood  screw,  having  had  its  head  rasped  or  filed  down 
till  the  head  of  the  shank  was  reduced  to  a  blunt  point,  was  driven  into  the  square  tube,  by  the 
pointed  shank,  not  far  from  the  eye  end.  The  screw  so  set  in  the  tube  was  embraced  by  a  long 
longitudinal  slot  made  in  the  lath.  The  slot,  while  wide  enough  to  admit  the  screw  bodily,  was 
narrow  enough  to  pinch  it  by  a  rather  gentle  pressure  due  to  the  elasticity  of  the  lath  alone.  This 
arrangement  was  effective  in  preventing  oscillations,  aud  allowed  the  telescope  to  be  moved  by 
hand  with  not  much  effort  and  not  much,  false  motion.  Screw  nuts  of  wood  were  provided,  by 
which  the  braces  could  be  clamped  at  the  slots,  but  these  were  not  used  any  further  than  they  may 
have  served  to  guard  against  the  lath  working  off  from  the  screw.  These  dispositions  were  all 
made  by  Professor  Newcomb,  and  were,  in  the  main,  executed  before  my  arrival. 

On  my  way  to  Des  Moines  it  occurred  to  me  that,  in  looking  after  the  space  immediately  con- 
tiguous to  the  sun's  luminous  surface  or  photosphere,  something  might  possibly  be  gained  by 
occupying  part  of  the  field  of  view  of  the  telescope  with  a  piece  of  colored  glass  or  smoked  mica, 
bounded  by  a  straight  edge.  The  crescent  of  the  uncovered  part  of  the  sun  could  then  be  viewed 
through  the  colored  glass,  and  on  bringing  the  cusp  near  to  the  edge  of  the  glass  we  would  avail 
ourselves  of  the  artifice  by  which  Dawes  made  his  discoveries  in  the  solar  spots,  and  Clark  brought 
to  light  the  companion  of  Sirius.  A  hasty  review  of  the  question  satisfied  me  that  before  totality 
at  Des  Moines  the  cusps  would  be  carried  eastward  across  a  line  nearly  parallel  to  the  line  joining 
them,  in  consequence  of  the  moon's  apparent  motion,  less  rapidly  than  the  sun  would  be  carried 
westward  across  the  same  line  by  his  diurnal  motion.  This  is  really  the  case,  but,  in  the  hurried 
judgment  which  alone  there  was  any  time  to  form,  I  somewhat  overrated  the  difference.  I  will  here 
give  the  comparison  which  I  have  made  since  the  eclipse,  at  the  same  time  making  plain  in  what 
manner  the  screen  glass  was  applied.  In  Fig  1,  let  C  represent  the  center  of  the  sun's  disk,  and 
about  the  same  center  let  F  B'N  E  be  a  circle  described  with 
a  radius  of  47".3,  the  quantity  by  which  the  apparent  semi- 
diameter  of  the  moon  seen  from  Des  Moines  at  totality 
exceeds  that  of  the  sun,  aud  let  A  B  D  E  be  the  apparent 
track  of  the  moon's  center  on  the  sun's  disk,  and  N  the  north 
point.  My  own  calculations  from  the  American  Nautical  i 
Almanac,  according  to  which  the  court-house  square  observa- 
tory in  Des  Moiues,  at  the  nearest  approach  of  centers,  was 
about  seven  miles  (.00176)  from  the  axis  of  the  shadow,  meas- 
ured at  right  angles,  give  N  C  B=63°  40',  and  N  C  E=100° 
44',  and  the  figure  is  drawn  to  the  true  proportions.  Now, 
suppose  a  circular  arc,  F  A,  whose  radius  is  equal  to  the 
radius  of  the  moon's  disk,  to  be  drawn  through  the  moon's 
center  at  A,  tangent  to  the  circle  F  B  N  E  at  F.  Then  it  is  evi- 
deut  that  if  the  radius  F  C  be  prolonged  through  G  it  will  meet  the  sun's  limb  at  the  cusp.  The 
motion  of  F  is,  therefore,  a  reduced  representation  of  that  of  the  cusp  reversed.  Drop  the  perpen- 
dicular F  L  upon  C  B.  B  L  differs  very  little,  especially  for  the  northern  cusp,  from  A  B,  so  long- 
as  the  crescent  is  less  than  70°  or  75°,  and  the  greatest  velocity  with  which  F  approaches  the  tan- 
gent line  H  B  K  is  very  nearly  the  velocity  of  the  moon's  center  along  A  B.  Hence  the  greatest 
velocity  with  which  the  cusp  crosses  a  line  parallel  to  H  B  K  is  such  a  velocity  as  would  traverse 
the  diameter  of  the  sun's  disk  in  about  the  period  of  1788,  which  it  would  take  the  moon's  center  to 
traverse  the  diameter  of  the  circle  F  B  N  E.  But  the  time  occupied  by  the  sun's  disk  in  crossing 
the  same  line  by  its  diurnal  motion  from  contact  to  contact  was  only  about  147s.  The  two  velocities 
are  nearly  in  the  ratio  of  six  to  five,  and  the  cusp  was,  at  the  near  approach  of  totality,  still  carried 
westward  across  a  fixed  line  parallel  to  H  B  K  with  a  velocity  about  one  sixth  that  of  the  diurnal 
motion  across  the  same  line.  The  angle  made  by  H  B  K  at  the  time  of  totality,  if  my  calculation 
is  correct,  with  the  sun's  vertical  diameter,  was  24°  51'  from  the  vertex  toward  the  right.  The 


OBSERVATIONS    OF   THE    ECLIPSE    OF   AUGUST   7,    1869. 


167 


FiK.  ' 


angle  at  which  the  straight  edge  of  the  colored  glass  was  set,  according  to  a  measurement  made 
after  the  eclipse,  was  23£°.  This  nearness  of  coincidence  was  in  part  accidental.  Moreover,  the 
inclination  of  the  glass  was  measured  with  the  telescope  horizontal,  and  wheu  pointed  to  the  sun 
(due  west  at  the  time  of  totality)  the  vertical  diameter  of  the  field  of  view  was  changed  by  nearly 
half  whatever  angle  of  azimuth  existed  between  the  meridian  and  the  horizontal  axis  of  the  gimbal 
on  which  the  telescope  moved.  This  angle,  however,  was  at  least  small,  if  it  existed  at  all. 

My  plan  of  observation  before  totality  was  to  set  the  telescope  with  the  cusp,  seen  through  the 
colored  glass,  approximated  as  closely  as  might  be  to  the  edge  of  the  glass,  and  then  allow  the  cusp 
to  approach  still  more  closely  to  the  edge  by  the  excess  of  the  diurnal  motion  across  it  over  the 
opposed  cusp  motion.  But  this  programme  was  not  as  closely  realized  as  it  might  have  been  had 
I  had  more  time  for  preparation,  and  for  careful  preliminary  study  of  the  conditions.  The  prepara- 
tion ought  to  have  been  so  complete  that  the  cusp  could  be  continuously  and  accurately  followed 
by  the  edge  of  the  glass. 

With  the  telescope  originally  intended  for  my  use  there  was  hardly  time  to  have  made  any 
preparation  at  all  for  this  way  of  observing,  there  not  being  at  hand  a  suitable  instrument-maker. 
But  the  temporary  arrangement  which  Professor  Xewcomb  placed  in  my  hands,  as  already 
described,  afforded  great  facility  for  carrying  it  hastily  into  effect  with  the  aid  merely  of  a  carpen- 
ter. The  colored  glass,  which  I  had  not  provided  myself  with  for  the  reason  that  the  method  did 
not  occur  to  me  till  after  I  was  on  my  way,  was  fortunately  at  the  disposal  of  Dr.  Hilgard,  of  St. 
Louis,  who  also  accompanied  the  expedition,  and  had  an  extra  glass  which  he  kindly  loaned  to  me 
for  the  occasion.  It  was  a  piece  of  deep-blue  plate-glass,  about  one-eighth  of  an  inch  thick,  as  near 
as  I  can  judge,  and  showed  the  sun's  disk  very  soft  and  easy  to  the  eye.  This  glass  is  shown  of 
half  size  at  a  b  c  d,  Fig.  2.  It  was  fastened  in  the  manner  there  shown  into  a  wooden  slider 
e  f  half  an  inch  thick,  also  shown  of  half  size,  as  is 
likewise  the  slot  g  h  I  A-  /  m,  with  some  enlargement  of 
the  latter  on  the  side  remote  from  the  eye.  The  dotted 
circle  q  r  shows  the  field  of  view  of  half  its  actual  size, 
and  by  moving  the  slider  along  the  line  e  f,  the  blue-f 
glass  abed  could  be  made  to  cover  the  entire  field  of 
view,  or  any  desired  part  of  the  field,  or  could  be 
thrown  entirely  out  of  the  field  on  either  side.  The  slider  e  f  was  applied  to  the  surface  of  the 
before-mentioned  square  piece  of  board  that  was  to  carry  the  eye-piece,  on  the  side,  of  course,  next 
the  eye,  and  was  held  in  place  by  a  wooden  cleat  laid  across  it  in  the  manner  shown  in  quarter 
size,  Fig.  3.  This  cleat  was  three-fourths  of  an  inch  thick,  and  was  screwed  to  the  square  piece 
of  board  after  having  been  recessed  half  an  inch  deep  so  as  to  Fig.  3. 

embrace  the  slider  without  undue  pressure,  and  the  Kamsden  eye- 
piece was  then  screwed  into  a  hole  cut  through  the  cleat.  Bearing 
in  mind  the  inversion  of  the  sun's  image,  the  left-hand  edge  a  6, 
Fig.  2,  of  the  blue  glass,  would  come  into  use  before  totality.  This 
edge  was,  therefore,  ground  straight  and  nearly  smooth  on  the  oil- 
stone. The  blue  glass  was  adjusted  to  the  focus  of  the  eye-piece,  and 
the  sun  was  afterwards  brought  into  focus  by  moving  the  square 
piece  of  board  a  little  to  and  fro  in  the  tube.  The  blue  glass  was 
much  thicker  than  it  would  have  been  desirable  to  employ  for  this 
purpose,  since  the  plate  displaces  the  focus  of  the  cone  of  rays 
traversing  it,  by  a  space  equal  to  one-third  its  thickness  for  glass, 
whose  index  of  refraction  is  1£.  Hence,  in  adjusting  the  solar  focus  some  time  before  totality, 
the  blue  plate  was  slid  entirely  from  the  field  of  view,  and  the  screen  glass  belonging  to  the  eye- 
piece, a  red  glass,  I  believe,  was  used  to  protect  the  eye  in  the  common  manner  by  placing  it  between 
the  eye  and  eye-lens.  This  was  done  with  a  view  to  leave  the  open  part  of  the  field  of  view  after- 
wards in  good  focus,  in  preference  to  the  part  which  would  be  covered  by  the  blue  glass  for  showing 
the  sun's  crescent.  Yet,  after  removing  the  red  glass  and  sliding  in  the  blue  glass,  the  definition  of 
the  details  of  the  solar  spots  appeared  equally  as  sharp  and  good  as  before,  and  my  inference  was  that 
the  eye  readily  accommodated  itself  to  the  difference  of  focus  produced.  Taking  the  change  in  the 


i 

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a.         d 

m 

168  REPORT    OF   MR.    J.    HOMER   LANE. 

place  of  the  focus  at  one  twenty-fifth  of  au  inch,  I  have  found,  by  direct  experiment  with  the  same 
eye-piece  since,  that  my  eye  does  readily  accommodate  itself  to  that  difference  of  focus.  As  the 
virtual  focal  distance  of  the  eye-piece  is  about  1.1  inch,  it  is  only  the  difference  between  the  stellar 
focus  of  the  reversed  eye-piece,  and  the  focus  of  the  same  for  an  object  at  twenty-nine  inches,  a 
range  easily  commanded  by  the  eyes  of  most  persons. 

These  things  being  arranged,  as  the  time  of  totality  drew  near,  the  blue  glass  entirely  covering 
the  field  of  view,  I  began  by  trying  the  skylight,  with  the  crescent  in  the  field,  by  a  cautious  side 
glance  of  the  eye  while  moving  the  blue  glass,  by  its  slider  e  /,  so  as  to  open  the  edge  of  the  field. 
The  light  was  yet  too  bright  for  the  eye  to  endure.  Soon  I  used  a  very  light  red  glass  as  a  protec- 
tion to  the  eye  in  these  trials.  As  soon  as  admissible  more  than  half  the  field  was  uncovered.  My 
attention  was  confined,  up  to  the  beginning  of  totality,  to  the  region  of  the  northern  cusp,  which, 
of  course,  as  inverted,  was  at  the  lower  side,  the  crescent  on  the  right.  At  last  the  moon's  limb  was 
seen  putting  boldly  out  into  the  open  field  beyond  the  blue  screen,  in  correspondence,  of  course, 
with  the  inner  limb  of  the  crescent.  The  time  of  this  was  101'  57m  19s  by  chronometer  Negus  No. 
1281,  which,  compared"  with  the  time  of  second  contact  as  noted  by  Professor  Hilgard,  gives  lra  13' 
before  totality.  Unluckily,  I  failed  to  recollect  positively  whether  the  light-red  screen  glass  was 
then  used.  My  impression  is  it  was  not,  and  it  certainly  was  not  afterwards.  The  moon's  limb,  as 
then  seen,  was  not  a  barely  percepible  outline,  but  was  abundantly  palpable  to  the  eye,  and  might 
evidently  have  been  seen  earlier.  Having  no  assistant,  I  think  I  must  have  taken  twelve  or  fifteen 
seconds  of  time  in  going  four  or  five  steps  to  the  chronometer  and  noting  the  time  with  due  care 
before  I  could  resume  my  place  at  the  telescope.  There  was,  therefore,  scarcely  over  a  minute  left 
before  the  beginning  of  totality,  perhaps  not  quite  that,  and  it  may  be  as  well  that,  in  the  anxiety 
of  the  moment,  1  did  not  know  the  time  was  so  short.  It  was  a  somewhat  hurried  work  to  bring 
the  cusp  to  close  proximity  to  the  edge  of  the  blue  screen  with  a  view  to  secure  a  review  of  as  much 
as  possible  of  the  moon's  limb  while  least  elevated  above  that  of  the  sun.  A  tolerably  good 
approximation  was  obtained,  but  some  few  degrees  of  the  moon's  limb  intervened  between  the  cusp 
and  the  edge  of  the  screen.  This  remark  will  at  least  apply  to  the  important  period  of  the  last  say 
ten  or  twelve  seconds  before  first  internal  contact,  perhaps  more.  The  excess  of  the  sun's  diurnal 
motion  across  the  edge  of  the  screen  over  the  cusp  motion  across  the  same  was  so  much  smaller 
than  my  first  rough  estimate  had  led  me  to  anticipate,  that  it  came  little,  if  any,  into  play  for 
bringing  the  cusp  up  to  the  edge,  but  this  same  circumstance  gave  a  useful  permanency  to  such  an 
approximation  as  I  did  obtain.  Of  course,  to  perfect  the  arrangement,  the  screen  should  have  been 
provided  with  a  slow  motion  for  readier  command  of  the  adjustment. 

After  the  moon's  limb  had  appeared  and  I  had  returned  from  noting  the  time,  and  had  got  the 
telescope  tolerably  readjusted,  I  looked  carefully  for  the  appearances  next  the  moon's  limb.  The 
light  of  the  corona  remained  almost  quenched  by  the  still  superior  light  of  the  sky.  It  had  been 
thought  possible  that  this  condition  might  afford  an  opportunity  to  see  the  regular  circular,  or  level 
outline,  of  a  low  solar  atmosphere,  if  such  existed  to  be  seen.  But  no  impression  of  such  an  appear- 
ance was  made  upon  my  eye.  .  None  of  the  light  above,  or  exterior  to,  the  moon's  limb,  that  I  no 
ticed,  prevailed  largely  over  the  light  of  the  sky,  until  within  some  five  to  eight  seconds,  as 
near  as  I  can  judge,  before  internal  contact  of  the  limbs ;  and  when  it  did  begin  to  prevail  it  blazed 
up  quite  rapidly  and  to  a  considerable  height  at  once,  say  from  10"  to  20",  yet  not,  as  it  struck  me, 
with  a  regular  outline.  The  general  impression  upon  me  of  this  first  outburst— for  it  was  only  a 
general  impression — was  more  as  if  it  was  built  up  of  tongues  of  flame.  The  brightness,  though  by  no 
means  dazzling,  was  such  as  to  make  it  not  impossible  that  some  kind  of  colored  screen  glass  might 
have  favored  the  observation  of  appearances  which  I  did  not  see.  The  color  appeared  mainly  white. 
The  estimate  of  10"  or  20"  for  the  height  could  not  be  made  at  the  time,  as  I  was  not  accustomed  to 
the  power  employed.  I  have  tried  to  form  a  rough  judgment  in  regard  to  it  since,  by  using  the 
same  eye-piece  with  the  objective  of  a  small  spy-glass,  to  view  a  circle  drawn  on  paper,  and  placed 
at  the  distance  where  it  gave  to  the  eye-piece  an  image  of  the  same  size  that  the  moon's  outline 
gave  in  the  telescope,  and  then  cutting  a  slit  in  the  paper  through  which  to  view  a  gas-light. 

In  these  observations  no  part  of  the  crescent  of  true  sunlight  got  beyond  the  blue  screen  into 
the  open  field.  In  the  last  second  or  two  before  totality,  the  length  of  arc  of  the  moon's  limb 
included  between  the  cusp  and  the  edge  of  the  screen  increased  very  rapidly ;  and  to  this  may 


OBSERVATIONS    OP    THE    ECLIPSE    OP   AUGUST    7,    1869.  169 

have  been  due  the  impression  produced  upon  me  that  the  cusp  ran  away  from  the  edge  of  the  screen, 
which  I  concluded  was  impossible,  if  the  edge  of  the  screen  was  really  set  parallel  to  the  tangent  at 
contact  of  limbs.  At  the  instant  of  contact  some  20°,  perhaps,  of  the  moon's  limb  (10°  on  each  side 
the  point  of  contact)  remained  behind  the  screen,  which  was  then  instantly  slid  entirely  from  the 
field  of  view.  [Nothing  was  now  seen  at  this  part  of  the  limb  to  modify  what  had  been  seen  before- 
Satisfied  of  this  I  swept  the  circuit  of  the  wonderful  spectacles  presented  in  the  corona,  but  returned 
immediately  to  the  very  peculiarly  formed  and  comparatively  small  red  clouds  first  seen  in  the  im- 
mediate region  of  the  point  of  first  internal  contact.  Leaving  to  others  the  sketching  of  the  general 
features  of  the  phenomenon,  I  selected  a  very  small  number  of  points  on  which  to  concentrate  my 
attention  with  a  view  to  watch  for  any  visible  changes.  In  this  I  was  partly  prompted  by  a  query 
which  had  rested  on  my  mind  for  two  or  three  months  previous — whether  the  coronal  light  might 
not  be  of  the  nature  of  our  auroras,  only  on  an  immensely  grander  scale.  One  or  two  of  these 
smaller  red  clouds  were  scrutinized  very  closely  for  some  time,  but  not  the  slightest  point  of  change 
was  detected.  The  several  clouds  at  this  part  of  the  limb  had  a  peculiarity  of  conformation  of  their 
own  which  seemed  to  distinguish  them  from  all  the  others  which  met  my  eye  in  sweeping  the  coro- 
na. The  somewhat  slender  elongated  body  curved  or  bent,  will  no  doubt  be  seen  in  the  photographs, 
in  one  of  which  in  fact,  seen  on  the  following  day,  I  recognized  these  bodies.  The  boundary  of  the 
cloud  seemed  to  be  quite  sharp  and  well  defined,  or  at  least  with  no  notable  shading  off.  This  I 
state  from  recollection,  and  not  from  any  note  purposely  taken  of  it  at  the  time. 

Becoming  convinced  that  the  red  clouds  I  was  scrutinizing  were  to  be  an  apparent  fixture  for 
the  period  of  totality,  I  turned  my  attention  to  the  agglomerations  of  white  light  in  the  corona,  and 
fixed  upon  two  of  these  which  were  remarkable  for  their  small  size  and  the  comparatively  dense 
accumulation  of  light  in  them.  These  were  situated  about  80°  from  the  vertex  toward  the  right, 
as  seen  inverted  in  the  telescope.  In  appearance  they  might  well  be  compared  to  small  telescopic 
comets  with  tails  of  some  length,  but  without  a  head,  and  with  no  distinct  indication  of  a  head  at 
one  end  rather  than  the  other.  They  were  not  far  from  radial  in  direction  relatively  to  the  sun's 
center — whether  exactly  so  I  did  not  remark  at  the  time — but  appeared  completely  isolated,  and 
had  their  origin  far  above  the  limb  of  the  moon ;  so  far,  at  least,  that  though  that  part  of  the  limb 
must  have  been  approaching  them,  if  their  height  above  the  sun's  limb  remained  constant,  the  ap- 
proach did  not  attract  my  attention.  I  referred  them  two  or  three  times  to  the  profile  of  neighbor- 
ing lunar  mountains,  so  far  as  to  make  it  evident  there  was  no  such  relative  motion  as  must  have 
been  expected  had  they  been  anything  floating  in  our  atmosphere.  They  manifestly  belonged  to  the 
heavens,  and  I  made  no  doubt  were  to  be  classed  with  the  other  parts  or  aggregations  of  white 
light  in  the  corona.  These  two  bodies  I  scrutinized  closely  for  some  time,  and,  as  I  suppose,  to  the 
end  of  totality.  The  form,  dimensions,  and  appearance  of  each,  and  their  distance  apart,  were  in 
constant  review ;  but  not  the  least  change  in  either  respect  was  seen.  It  would  be  in  vain  for  me  to 
try  to  estimate  the  length  of  time  occupied  either  with  these  objects  or  with  the  red  clouds  particularly 
watched.  As  to  the  distance  apart  of  these  two  white  comet-like  objects,  I  judged,  after  the  largest 
solar  spot  had  been  uncovered,  that  they  would  have  included  between  their  centers  the  nucleus  of 
that  spot,  but  not  the  penumbra.  I  had  no  means  of  taking  any  measures,  nor  would  it  have  been 
easy  to  take  measures  without  sacrificing  the  watch  for  the  presence  or  absence  of  changes.  In 
order,  however,  to  reproduce  as  near  as  practicable  what  I  saw,  I  have  laid  down  upon  paper  a  circle 
of  the  same  size  that  the  moon's  outline  had  in  the  focus  of  the  object-glass — almost  an  inch — and 
holding  this  up  to  the  light  in  the  field  of  view  of  the  same  eye-piece  used  in  the  telescope,  have 
tried  to  lay  down  with  a  pencil  the  dimensions  and  situations  of  the  two  objects.  The  following  is 
the  result  I  got  in  this  way: 

Length  of  each  cometoid  light,  130". 

Height  of  its  origin  above  moon's  limb,  100"  to  80". 

Distance  from  center  to  center  of  the  two,  50"  to  40". 

Perhaps  the  height  above  the  moon's  limb  should  be  taken  at  about  half  a  minute  before  the 
end  of  totality.  The  estimate  of  50"  to  40"  here  made  for  the  distance  apart  of  the  two  objects  may 
be  considered  entirely  independent  of  the  one  first  given  referring  to  the  solar  spot.  In  that  case  the 

22* 


170  REPORT  OF  MR.  J.  HOMER  LANE. 

judgment  comparing  with  tbe  spot  AN  as  checked  by  selecting  a  pair  of  scratches  on  the  blue  screen 
glass  in  the  field  of  view,  before  the  eclipse  was  over,  whose  interval  was  judged  not  far  from  equal 
to  that  of  the  two  objects,  and  then  bringing  the  solar  spot  between  them. 

The  end  of  totality  having  arrived,  I  thought  it  well  to  ascertain  how  long  the  eastern,  or  far 
limb,  of  the  moon  could  be  seen.  With  this  view  I  continued  to  watch  that  part  of  tbe  limb  coin 
prising  most  of  the  lower  right-hand  quadrant,  and  some  adjoining  part,  perhaps,  of  the  upper 
right-hand  quadrant,  as  seen  inverted  in  the  telescope.  For  some  little  time  it  continued  to  be 
strongly  marked ;  for  a  considerable  length  of  time  it  was  easily  seen ;  and  for  a  still  longer  time  it 
could  be  unmistakably  followed  by  the  aid  of  a  little  motion  given  to  the  telescope.  As  the  last 
faint  traces  were  being  obliterated  I  noted  the  time  by  Negus  No.  1281,  11"  3m  30».  Comparing 
this  with  the  time  of  third  contact  as  noted  by  Professor  Hilgard,  I  And  it  to  have  been  2™  5"  after 
the  end  of  totality.  This  time  is  so  considerable  that  unless  the  observation  has  been  confirmed  by 
others,  I  would  not  wonder  if  it  should  be  thought  liable  to  the  uncertainty  that  I  might  have  made 
a  mistake  in  noting  the  minute.  I  can  only  say  that  I  tried  to  take  good  care  in  noting  the 
minute,  and  that  I  have  no  reason  to  doubt  the  time  is  as  1  have  given  it. 
Respectfully  submitted. 

J.  HOSIER   LANE. 

Commodore  B.  F.  SANDS,  U.  S.  N., 

Superintendent  U.  S.  Naval  Observatory,  Waxhington,  D.  C. 


OF 


MR.  ¥.  S.   GILMAI,  JR. 


REPORT    OF    MR.    W.    S.    GIL  MAN,  JR. 


Sioux  CITY,  IOWA,  August  10, 1869. 

DEAR  SIR  :  I  Laud  you  herewith  a  report  of  the  total  eclipse  of  the  sun  on  the  7th  instant,  as 
observed  by  myself  and  eight  others  at  St.  Paul  Junction,  Plymouth  County,  Iowa,  twenty-five 
miles  northeast  of  this  place. 

I  took  up  niy  position  on  the  4th  instant,  on  the  northeast  quarter  of  section  16,  township  92 
north,  range  45  west,  and  estimated  my  longitude  to  be  19°  5'  45"  west  of  Washington,  assuming 
16°  34'  1".4  to  be  the  longitude  of  Des  Moines.  My  latitude  I  estimated  at  42°  47'  30"  north.  In 
arriving  at  these  values  I  used  the  new  map  of  Iowa,  issued  the  present  summer  by  Colton,  of 
New  York. 

My  telescope  was  set  upon  the  west  side  of  the  house  of  Mr.  N.  E.  Farrell,  at  a  point  twelve  feet 
south  of  the  north  line  of  section  16,  and  seventy-five  feet  east  of  the  west  line  of  the  same  section. 

DESCRIPTION  OF  INSTRUMENTS. 

There  were  in  the  party  three  small  telescopes,  of  apertures  varying  from  1  to  1.2  inches  and 
magnifying  from  eight  to  ten  times.  I  had  brought  with  me  my  4-inch  telescope,  made  by  Alvan 
Clark,  of  Cambridgeport.  Beside  these  instruments  we  had  a  good  binocular  field-glass. 

All  the  instruments  were  substantially  mounted  on  tripods  or  steady  rests,  in  such  a  manner 
as  to  allow  of  easy  movement  in  any  desired  direction,  and  their  eye-pieces  were  slightly  smoked. 
Neutral  tinted  shades  and  deeply  smoked  glass  were  also  used  during  the  earlier  and  later  portions 
of  the  eclipse. 

By  means  of  a  good  thermometer,  of  B.  Pike's  make,  I  took  record  of  temperatures  for  several 
days  preceding  and  following  the  eclipse,  as  will  be  found  on  reference  to  Schedule  A.  The  ther- 
mometer was  exposed  to  the  weather  on  the  north  side  of  Mr.  FarrelFs  house,  and  screened  only 
from  direct  light  of  sun.  Its  height  above  the  ground  was  five  feet  six  inches. 

When  noting  contacts  I  used  S.  Hammond's  mean  time  gold  chronometer,  No.  300,  which  lost 
18.86  per  diem. 

The  instruments  were  distributed  as  follows: 

I  observed  with  my  admirably  defining  4-inch  achromatic  of  five  feet  two  inches  focal  length, 
charged  with  a  power  of  fifty,  and  carrying  a  ruled  micrometer  of  glass,  giving  angles  of  position 
for  every  45°,  and  measuring  arcs  of  15"  when  used  in  connection  with  my  instrument.  My  mount- 
ing was  Mr.  Clark's  usual  portable  equatorial,  without  circles  or  clock  work.  The  power  I  employed 
gave  a  field  of  view  of  about  43'  of  arc. 

My  principal  aim  was  to  get  observations  of  (1)  the  times  of  contact;  (2)  the  size  and  positions 
of  red  flames;  (3)  the  outline  and  general  extent  of  the  corona,  and  (4)  the  colors  of  both  the  flames 
and  the  corona. 

Daniel  T.  Oilman  confined  himself  to  noting  time  by  the  chronometer,  for  which  he  had  been 
qualified  by  previous  practice  with  me. 

N.  E.  Farrell,  a  member  of  the  Powell  Colorado  exploring  expedition  of  1868,  kept  the  record 
of  the  thermometer.  He  used  a  field-glass  at  various  times,  to  which  instrument  he  was  well 
accustomed,  having  employed  it  constantly  during  the  expedition  referred  to. 

Leon  Vincent,  of  the  civil  engineer  corps  of  the  Iowa  Falls  and  Sioux  City  railroad,  employed 
a  telescope,  with  which  he  was  well  acquainted,  having  an  aperture  of  1.1  inches,  and  a  focal  length 
of  10  inches.  It  gave  a  direct  image,  and  magnified  about  ten  times. 

Lucius  C.  Phelps,  associated  with  the  above  in  the  engineer  corps,  used  a  telescope  of  J-iiich 
aperture,  having  a  focal  length  of  10  inches,  and  magnifying  about  ten  times.  This  instrument 
gave  an  inverted  image. 

Vincent  Wood  used  a  telescope  of  1.2  inches  aperture  and  20  inches  focal  length,  which  gave 
a  direct  image.  The  power  of  this  telescope  was  a  little,  though  not  much,  above  the  two  just 
mentioned. 


174 


REPORT    OF   MR.   W.   S.   OILMAN,    JR. 


Eugene  Lockliii  and  Seymour  Ball  observed  without  instruments  for  flames,  extent  of  corona, 
stars,  and  planets.  Mrs.  N.  E.  Farrell  observed  especially  for  the  approach  of  the  dark  shadow  in 
the  air,  for  stars  and  planets,  and  assisted  in  keeping  the  thermometrical  record. 

Specific  duties  were  assigned  to  each  of  the  above  by  written  schedules,  which  were  carefully 
studied  a  day  or  two  previously. 

WEATHEB  DURING  THE  ECLIPSE. 

At  2  p.  in.  the  sky  cleared  overhead,  and  at  3  p.  m.  there  were  no  clouds.  A  slight  haze 
remained,  which  assisted  the  definition  of  our  instruments.  On  the  southeast  horizon  the  hnze 
was  thick  and  resembled  a  fog-bank. 

THE  ECLIPSE— FIRST  CONTACT. 

At  4h  57m  9s  by  my  chronometer,  (see  Schedule  B,)  I  observed  with  my  telescope  a  small 
black  speck  on  the  preceding  limb  of  the  sun's  disk,  at  the  precise  point  to  which  I  had  been  for 
some  minutes  directing  my  attention.  At  first  I  took  it  to  be  the  result  of  a  slight  tremor  of  the 
sun's  limb  produced  by  an  atmospheric  cause,  though  at  the  time  the  atmosphere  was  steady  and 
the  definition  all  that  could  be  desired. 


s. 


w. 


E. 


W. 


N. 
I. 

FIRST    CONTACT,  4*1.  57m.  95.  N.  Y.  M.  T. 

At  4h  57m  12s.o,  or  3.5  seconds  later  than  the  above 
time,  the  impinging  limb  of  the  moon  rendered  the  nature 
of  the  black  point  apparent.  The  appearance  of  this 
small  point  is  given  in  the  above  sketch,  No.  1,  in  which 
is  also  shown  the  moon's  limb,  visible  away  from  the 
sun's  disk  a  few  minutes  from  the  point  of  contact  on 
either  side.  Though  I  had  looked  with  great  care  for  the 
approaching  moon  some  minutes  previous  to  contact,  I 


N. 
2. 

APPEARANCE    OF   THE    SUN'S   DISC    AT 

5(1.  5m.  N.  Y.   M.  T.,   SHOWING    FOUR    PROJECTIONS 

ON    THE    MOON'S   LIMB. 

saw  nothing  of  it  until  after  1  had  seized 

the  black  excrescence  represented  in  the  sketch,  (No.  1.)  Mr.  Farrell  noted  the  time  of  first  contact 
independently,  by  means  of  his  field-glass,  at  41'  57m  18s  chronometer  time,  or  9  seconds  later  than 
myself. 

As  the  moon  advanced  on  the  sun's  disk,  it  was  apparent  that  its  limb  was  very  rough.  I  made 
a  sketch  of  its  appearance  at  5h  5m  chronometer  time,  which  I  append  herewith,  (No.  2.) 

There  were  distinctly  visible  at  this  time  near  the  center  of  the  dark  limb  of  the  moon  four 
projections  of  unequal  altitude  and  varying  extent.  The  second  prominence  from  the  north  Avas 
the  highest,  and  measured  about  three  seconds  of  arc,  as  nearly  as  I  could  estimate.  It  was  this 


OBSERVATIONS    OF   THE    ECLIPSE    OF   AUGUST   7,    1869. 


175 


poiut  which  first  touched  the  sun's  disk,  as  shown  in  sketch  No.  1.  I  suppose  these  elevations  to 
have  been  the  Montos  d'Alembert  of  Beer  &  Mueller's  large  map  of  the  moon.  I  roughly  estimated 
that  the  distance  from  I)  to  A  was  about  1',  from  C  to  B  1'.25,  while  the  two  sets  of  prominences 
appeared  to  be  separated  by  an  interval  of  1'.75.  The  ridge  at  B  was  of  greater  extent  and  more 
jagged  than  the  others,  though  not  so  high  in  relief  above  the  moon's  surface  as  that  marked  A. 
These  ridges  were  witnessed  by  several  persons  at  various  times,  all  agreeing  both  as  regards  their 
number  and  relative  distances.  They  were  seen  during  the  entire  transit  of  the  moon's  following 
limb. 


SPOTS  ON  THE  SUN. 

There  were,  during  the  eclipse,  four  groups  of  spots  upon 
located  on  a  diagram  during  the  hour  pre- 
ceding the  first  contact,  with  the  intention 
of  recording  their  exact  times  of  disappear- 
ance and  reappearance.  Sketch  No.  3  is  a 
copy  of  this  diagram.  1  have  numbered  the 
groups  from  1  to  4,  and  reckoned  the  times 
of  disappearance  and  reappearance  from 
those  portions  of  the  groups  indicated  by  a 
cross,  (x). 

In  group  No.  1  I  reckoned  the  disap- 
pearance from  the  minute  bright  point  in  the 
penumbra  of  the  large  spot  on  the  following 
side  of  the  phenomenon.  This  point  of  bright 
matter  was  an  interesting  object.  The  details 
of  the  spot  are  given  in  the  corner  of  Sketch 
No.  3.  In  estimating  the  disappearance  and 
reappearance  of  group  No.  3, 1  reckoned  from 
the  larger  of  the  two  following  spots  on  this 
triple  group.  In  group  No.  2 1  took  the  largest 
spot  on  the  following  side  of  the  group.  In 
group  No.  4 — a  remarkable  object,  by  the 
way,  of  which  more  anon — I  selected  the 
southern  edge  of  the  umbra  of  the  great  spot. 
The  times  will  be  found  in  Schedule  B. 


the  sun's  disk,  all  of  which  I 

s 


had 


DIAGRAM  SHOWING  SPOTS  ON  THE  SUN  DURING  THE 
ECLIPSE,  .AS  SKETCHED  ONE  HOUR  PREVIOUS  TO  THE 
FIRST  CONTACT. 


APPEARANCE  OF  THE  SOLAR  SURFACE. 

Many  times  during  the  progress  of  the  eclipse  was  my  attention  arrested  by  the  striking  appear- 
ance of  the  surface  of  the  sun.  The  pores  of  the  photosphere  were  visible,  with  unusual  distinctness, 
to  within  a  few  seconds  of  the  edges  of  the  penumbrae  surrounding  the  larger  spots.  This  phenom- 
enon was  more  striking  as  the  eclipse  progressed.  The  facula?  clustering  around  the  large  spot 
numbered  4  in  the  diagram  were  very  prominent,  and  suggested  the  comparison  to  lumps  of  plastic 
white  clay,  or  plaster  of  Paris,  scattered  around  its  borders,  or  to  the  little  lunar  peaks  in  the 
vicinity  of  Plato  and  <  'assini,  as  they  appear  when  just  within  the  illuminated  portion  of  the  moon's 
disk,  at  the  first  quarter.  The  encircling  ridges  of  facuhe  seemed  to  stand  out  in  bold  relief  from 
the  sun's  general  surface. 

APPROACH  OF  THE  TOTAL  PHASE. 

At  oh  401"  chronometer  time,  which  was  twenty  minutes  previous  to  totality,  cocks  were  heard 
to  crow,  and  chickens  prepared  for  the  night.  A  herd  of  cattle  also  came  in  from  the  prairies, 
where  they  had  been  feeding  all  day,  and  went  into  the  barn-yard  near  by. 

At  511  48m  chronometer  time,  the  gloom  deepened  rapidly,  and  the  sudden  coolness  of  the 
atmosphere  struck  me  with  surprise.  The  feeling  was  as  if  one  was  about  to  enter  a  cavern. 


176  REPORT    OF    MR.    W.   S.    OILMAN,    JR. 

A  few  minutes  previous  to  totality  the  horizon  changed  color,  as  it  is  frequently  seen  to  do  on 
the  approach  of  a  storm.  To  the  south  the  sky  became  of  a  rose-violet  hue  at  30°  from  the  horizon. 
At  the  same  elevation  in  the  northwest  a  grayish-violet  tint  prevailed. 

Perfect  silence  reigned  during  the  remaining  moments  of  sunlight,  and  continued  even  for  some 
instants  after  the  subsequent  captivating  scene  of  beauty  burst  upon  our  sight.  During  this  still- 
ness Mrs.  Farrell  distinctly  saw  the  moon's  shadow  rapidly  approach- 
ing in  the  air.  It  appeared  to  go  upwards  from  the  western  horizon 
like  the  lifting  of  a  dark  curtain. 

As  the  thin  solar  crescent  was  about  to  vanish  I  watched  care- 
fully for  the  phenomenon  of  Baily's  Beads.  The  atmosphere  was 
very  steady,  and  the  limbs  of  both  sun  and  moon  were  admirably 
defined.  The  roughness  of  the  moon's  limb  produced  an  approach 
to  the  phenomenon  as  the  several  projections  closed  in  upon  the 
remnant  of  the  solar  disk,  but  no  appearance  of  beads  was  noticed. 
With  a  less  favoring  atmosphere  I  doubt  not  the  sight  would  have 
been  witnessed.  Mr.  Farrell,  however,  using  a  field-glass,  noticed 
the  beads,  and  compared  them  to  drops  of  water  running  together 


and  quickly  disappearing.    He  made  the  annexed  sketch  of  the          PARALLEL  TO 
phenomenon  in  my  note-book  soon  after  the  ending  of  the  eclipse.  4 

MINUTE  CRESCENT  NEAR  THE  SUN. 

About  half  a  minute  preceding  totality,  possibly  somewhat  less,  Mr.  Vincent  left  his  position 
and  came  to  me  exclaiming  that  he  saw  a  miniature  crescent-shaped  star  under  the  moon,  and  that 
1  must  come  and  verify  his  observation.  So  interested  was  I  in  my  own  work  that  I  paid  little 
attention  to  Mr.  Vincent's  announcement,  but  on  his  returning  a  second  time,  more  urgent  than 
ever  to  have  me  look  at  the  object,  I  did  so  in  a  hurried  manner,  using  his  glass.  I  detected  nothing 
in  the  few  seconds  I  gave  to  the  search. 

According  to  Mr.  Vincent's  drawing,  made  soon  after  the  eclipse,  the  little  moon  was  located 
one  and  a  half  times  the  moon's  diameter  from  its  limb,  and  to  the  left  of  a  line  drawn  perpendicu 
larly  down  to  the  horizon.    I  do  not  think  I  searched  the  sky  as  far  away  from  the  moon  as  the 
distance  given.    During  totality  the  object  was  forgotten,  but  shortly  after  the  third  contact  lie 
readily  picked  it  up  in  the  same  locality. 

TOTALITY. 

The  second  contact,  which  was  well  observed,  took  plack  at  61'  Om  45S.5  chronometer  time. 
Owing  to  an  unfortunate  error  in  my  not  removing  the  dark  shade  instantly  on  the  extinction  of 
the  sun,  I  saw  nothing  of  the  formation  of  the  corona.  The  gradual  appearance  of  this  beautiful 
feature  of  the  eclipse  was  observed  by  Messrs.  Farrell  and  Vincent.  An  anvil-shaped  rose-colored 
flame  or  protuberance  and  a  large  portion  of  the  corona  'if  ere  seen  several  seconds  previous  to  the  xcronil 
contact. 

As  soon  as  I  had  removed  my  dark  shade  the  view  presented  to  my  eye  in  the  telescope  was 
one  of  indescribable  beauty.  My  attention  was  chiefly  attracted  to  the  large  anvil-shaped  protuber- 
ance, which  I  at  once  recognized  as  occupying  that  portion  of  the  sun's  limb  in  the  region  of  which 
I  had  previously  seen  the  brightest  double  facuia,  indicated  in  Sketch  3  by  the  letter  B.  It  appeared 
like  a  monstrous  glowing  coal,  dotted  here  and  there,  particularly  on  the  southern  side,  with  minute 
flakes  of  brilliant  deep  crimson.  It  was  my  expectation  that  the  rich  masses  of  facuia!  visible  in  the 
sun's  southern  hemisphere,  near  the  eastern  limb,  on  the  26th  of  July  last,  and  indicated  by  the  let- 
ter A  in  Sketches  5  and  G,  would  be  near  the  western  limb  on  the  day  of  the  solar  eclipse.  The 
appearance  of  striking  rose-colored  flames  in  this  vicinity  would,  it  seemed  to  me,  render  plausible 
the  theory  of  a  connection  between  these  objects  and  portions  of  the  sun's  surface  that  have  the 


OBSERVATIONS    OF    THE    ECLIPSE    OF    AUGUST    7,    1809. 


177 


appearance  of  being  unusually  agitated.  It  was,  therefore,  with  considerable  interest  that  I  noticed 
on  tlie  5th,  Cth,  and  7th  of  August,  in  the  southwestern  quadrant  of  the  sun,  intensely  bright,  white 
ridges  approaching  the  limb,  as  represented  in  Sketches  7,  8,  and  3. 

s. 


JULY  j6<J  6>>.  W.  M.T. 


TWO    SPOTS   AT  A   SURROUNDED  BY    FACULAE.      NO    FACULAE 

DETECTED     ELSEWHERE.  OBSERVATION     MADE     THROUGH 

CLOUDS       BEAUTIFUL    LINE    OF    SMALL    BLACK  POINTS  AT  B. 


W. 


THREE  SPOTS  WELL  SEEN  THROUGH  CLOUDS.      FACULAE 
SURROUNDING  A  AND  FOLLOWING.    FACULAE  DISTINCT  AT  B. 


AUG. 


.  W.  M.T. 


AUG.  6d  •  4h.  W.  M.T 


FACULAE  FROM  235-  TO  270'.  AND  VERY  MARKED  AT  245-. 
TWO  BRIGHT  MASSES  AT  LATTER  POINT.  SPOTS  AT  B.  C.  &  D. 
AT  C,  SPOT  OF  CONSIDERABLE  SIZE  AND  INTEREST.  NO  FA- 
CULAE SEEN  IN  NORTHERN  HEMISPHERE. 

7 


TWO    BRILLIANT    FACULAE    AT  250"  (?)   DIFFICULT    OBSERVATION 
OWING   TO    CLOUDS. 


N. 

So  deep  was  my  interest  in  the  subject  that  I  had  made  the  condition  of  the  solar  disk  a  study 
from  the  middle  of  June  to  the  first  week  of  August,  and  especially  on  the  24th,  25th,  and  2Gth  of 
July  and  the  5th  of  August,  with  a  view  of  forecasting  the,  positions  of  protuberances  during  the 
23* 


178 


REPORT    OF    MR.    W.    S.    OILMAN,    JR. 


eclipse,  which  forecast  I  made  on  the  after- 
noon of  the  5th,  as  given  in  Sketch  9,  herewith- 
The  impression  upon  my  mind  has,  for  a  long- 
time, been  that  the  rose  protuberances  are  in 
the  nature  of  exhalations  from  portions  of  the 
surface  in  a  high  state  of  agitation,  such  as 
witnessed  in  the  vicinity  of  faculous  ridges 
and  spots. 

Having  made  the  forecast  referred  to,  I 
indicated  with. a  cross  (x)  two  prominences  w 
which,  I  expected,  might  be  unusually  large. 
The  eastern  one  of  these  would,  as  I  thought, 
be  produced  through  the  medium  ot  the  agi- 
tated ridges  at  D,  pictured  in  Sketches  10  and 
11,  which,  on  the  afternoon  of  the  7th  of  Au- 
gust, would,  if  sufficiently  persistent,  occupy, 
by  virtue  of  the  sun's  revolution,  a  position  on 
the  eastern  limb,  say  near  25°  north  latitude. 

The  western  flame,  which  I  marked  in  the 
same  manner,  was  located  in  south  latitude 
10°,  for  the  reason  that  the  large  spot  at  B, 
Sketch  7,  would,  from  the  same  cause,  during 
the  eclipse,  occupy  this  portion  of  the  sun's  limb,  and  from  it 
tions  that  would  be  readilv  visible. 


N. 

ROSE    PROTUBERANCES   AS   FORECASTED 
AUGUST    5,    .869. 

I  surmised  there  would  be  exhala- 


W 


JULY  ?4<i 


W.  M.  T. 


TWO  SPOTS  AT  A  FOLLOWED  BY  BRIGHT  FACULAE. 
FACULAE  VERY  BRIGHT  AT  C,  D  &  E,  ESPECIALLY  AT  D. 
AT  p.  2'  FROM  LIMB,  TWO  BRIGHT  MASSES  OF  FACULAE. 
VERY  MUCH  CONDENSED. 


IO 


JULY    25<<.   ih.  W.   M.  T. 


NlP 


A  BRIGHT  RIDGE  OF  FACULAE  HAS  JUST  APPEARED 
UNDER  THE  EQUATOR  ON  EASTERN  LIMB  AT  G.  BRIGHT 
RIDGE  ALSO  AT  H.  FOLLOWING  A,  FACULAE  MORE  BRIL 
LIANT.  ATMOSPHERE  HAZY 


N. 

The  first  of  these  marked  flames  I  failed  to  verify,  though  it  may  have  been  seen  by  others.  1 
have,  the  more  hope  that  this  will  prove  the  case  since  out  of  six  protuberances  seen  by  me  I  noted 
the  positions  of  but  four  from  want  of  time. 

In  regard  to  the  second  marked  flame,  this  also  was  not  seen,  and  doubtless  had  no  existence, 
as  the  locality  was  carefully  studied  by  me,  and  but  one  flame  (A)  appeared  in  this,  the  southwest- 
ern quadrant  of  the  sun.  The  protuberance,  however,  located  over  the  bright  double  facula  further 
south,  was  the  great  anvil-shaped  flame  already  noticed. .  The  fact  of  the  utter  absence  of  rosy  mat- 
ter in  the  vicinity  of  the  spot  may  indicate  an  imcard  current  in  the  case  of  spot  openings  in  oppo- 


OBSERVATIONS    OF    THE    ECLIPSE    OF   AUGUST   7,    1869. 


179 


sitiou  to  aii  out  tea  rd  or  upward  OIK-  iu  the  case  of  factilous  agitations.  The  pointing  of  the  anvil 
toward  the  equator  may  in  this  connection  possess  some  significance,  indicating,  possibly,  a  mon- 
ster current  toward  the  large  spot  13,  under  the  Equator. 

I  have  reason  for  believing  that  the  protuberances  forecasted  at  B,  (',  and  D  had  their  true 
counterparts  in  those  observed  during  the.  eclipse,  as  represented  in  Sketches  1^2.  13,  and  14.     I 

s. 


i?   B 


ROSY    PROMINENCES   AI 
6h.   im.45s N.  Y.  M.  T       TREMULOUS    LIGHT    AT    A. 


ROSY    PROMINENCES   AT 

6h.  am.    15,.  N.  Y.  M.  T.       NORTHERN    END    OF    A    COM- 
POSED   OF    FIBROUS   LINES    OF    FLAME. 


West. 


•     ROSY    PROMINENCES    AT 
«h.  am.  455.  N.  Y.  M.  T.      NEW    FLAME    AT    D. 


East. 


N. 

should  here  remark,  that  having  made  my  forecast,  I  laid  it  away  in  my  portfolio,  where  it  was  not 
disturbed  until  the  morning  of  the  9th,  when  I  first  became  aware  of  the  coincidences  referred  to. 

The  protuberances  were  uniformly  of  an  orange  color,  and,  as  It  seemed  to  me,  of  the  precise 
tint  of  the  glowing  coals  in  an  anthracite  grate.  There  was,  however,  in  the  case  of  the  three  north- 
ern protuberances,  at  least,  the  remarkable  addition  of  small  crimson  scales  or  flakes  of  astonishing 
richness  of  color.  These  scales  seemed  to  have  no  connection  with  the  protuberances,  though  they 
were  projected  upon  them.  They  were  not  seen,  however,  disconnected  from  the  flames,  and  their 
separate  character  may  have  been  more  apparent  than  real.  I  was  deeply  interested  in  them,  and 
have  no  doubt  that  the  phenomenon  of  crimson  flakes  was  truly  witnessed,  and  that  my  eyes 
were  not  deceived. 


180  REPORT    OF   MR.    W     S.    GILMAN,  JR. 

At  the  bases  of  the  flames  sulphurous  lines  were  discernible,  as  also  at  the  tapering,  "  wispy'7 
eud  of  the  anvil-shaped  mass  pointing  to  the  equator.  I  saw  no  changes  in  any  of  the  llames,  except 
an  apparent  wavy  motion  in  the  pointed  end  of  the  large  one.  Though  I  have  called  them  inter- 
changeably flame*  and  protuberances,  they  did  not  appear  like  names,  but  possessed  a  clear,  unchang- 
ing, almost  harsh  outline,  as  if  cut  out  of  some  solid  substance.  1  noticed  a  llaky  structure  in  the 
large  protuberance,  and  was  strongly  impressed  with  its  resemblance  to  glowing  embers,  dotted 
over  with  minute  crimson  spots,  as  stated.  I  was  not  prepared  for  such  stability  on  the  part  of  the 
protuberances  as  was  witnessed. 

I  made  the  positions  of  the  four  protuberances  by  estimation  as  follows,  vi/. : 

A,  anvil-shaped  mass,  230°— 235° 

B,  140 

Q,  120 

D,  320 

THE  COKONA. 

The  general  outline  of  the  corona  was  a  trapezium,  with  the  widest  side  to  the  southeast.  (See 
Plate  XII.)  There  were  also  lesser  projections  on  the  four  sides,  as  well  as  several  small  indentations. 
The  longest  masses  of  light  coincided  very  nearly  with  the  north  and  east  points,  at  the  middle  of 
totality.  Mr.  Farrell  also  noted  the  same  peculiarity. 

The  corona  was  composed  of  an  infinitude  of  fine  violet,  mauve-colored,  white,  and  yellowish 
white  rays,  issuing  from  behind  the  moon.  I  detected  no  clouds  in  it.  The  exterior  edge  was  very 
jagged  in  appearance,  but  did  not  possess  a  harsh  outline,  having,  on  the  contrary,  a  soft  blurred 
look.  This  was  quite  contrary  to  my  expectations,  as,  from  all  the  drawings  of  eclipses  1  had  ever 
seen,  I  was  led  to  expect  a  well-defined  and  truly  circular  halo  of  light,  extending  to  an  equal  dis 
tance  on  all  sides. 

Mr.  Farrell  described  the  appearance  of  the  corona  verbally,  as  follows:  "It  was  a  silvery-gray 
crown  of  light,  and  looked  as  if  it  was  the  product  of  countless  fine  jets  of  steam,  issuing  from  be- 
hind a  dark  globe.  Near  the  moon's  disk,  the  light  seemed  almost  phosphorescent." 

During  totality  the  seconds  on  our  watch  faces  could  not  be  read  without  the  assistance  of  the 
lamps  placed  in  the  windows  of  the  house  to  aid  us  at  this  juncture.  The  time  could  with  difficulty 
be  told  by  the  larger  hands. 

MINUTE  OBJECT  SEEN  NEAR  THE  SUN. 

A  few  moments  after  the  formation  of  the  corona,  a  minute  object  was  noted  independently  by 
four  of  the  party,  and  should  be  here  mentioned. 

A  small  but  exceedingly  bright  point,  like  a  star,  was  witnessed  by  Messrs.  Farrell,  Phelps. 
and  Locklin,  and  Mrs.  Farrell,  during  the  period  of  totality.  It  appeared  near  the  limits  of  the 
corona,  below  the  moon's  disk — direct  vision — and  in  the  region  of  the  anvil-shaped  protuberance. 
Mr.  Farrel  judged  it  to  be  about  one-sixth — some  say  one-tenth— the  size  of  Mercury ;  which  latter 
star  was  almost  directly  to  the  right  of  it,  on  a  line  parallel  to  the  horizon. 

With  the  exception  of  Mrs.  Farrell,  all  located  the  star  a  little  to  the  right  of  the  red  promi- 
nence, or  at  about  230°  from  the  north  point,  reckoning  by  the  east.  Each  of  the  observers  men 
tioned  feels  very  positive  that  what  he  saw  was  truly  a  star. 

I  cannot  connect  Mr.  Vincent's  miniature  crescent  with  the  small  star  of  Messrs.  Farrell,  Phelps, 
and  others,  though,  owing  to  Mr.  Vincent's  peculiar  position,  he  may  have  located  his  object  too  far 
to  the  left.  He  was  leaning  on  his  left  arm  which  may  have  led  him  to  form  in  his  mind  a  horizon 
inclining  considerably  to  the  true  one.  This  would  cause  the  location  of  a  star  below  the  sun  to  be 
too  far  to  the  left  in  his  diagram.  He  estimated  the  object  seen  by  him  as  three  times  as  far  re- 
moved from  the  moon's  limb  as  the  star  noted  by  Messrs.  Farrell,  Phelps,  ami  others.  The  report 
of  each  observer  was  given  to  me  shortly  after  the  termination  of  the  eclipse,  and  not  iu  the  hearing 
of  others. 


OBSERVATIONS    OF  THE   ECLIPSE   OF  AUGUST   7,   1869.  181 

PLANETS  AND  STARS  VISIBLE. 

Of  the  planets  and  stars  1  saw  but  Venus.  Regains,  and  Mercury.  At  no  time  during  the 
eclipse  did  it  occur  to  me  to  look  for  intra-niercurial  planets.  I  saw  Regulus  with  difficulty  as  a 
glimpse  star,  with  the  unaided  eye.  The  reports  show  that  seven  stars  were  witnessed  by  our 
party,  if  we  include  the  little  brilliant  below  the  snn. 

The  gloom  of  totality  did  not  impress  me  as  being  at  all  like  that  of  moonlight,  but  rather  like 
the  somber  light  of  an  approaching  thunder-storm,  with  this  remarkable  addition :  an  indescribably 
delicate  mauve  or  violet-tinted  glow  in  the  portion  of  the  heavens  occupied  by  the  eclipsed  sun. 

Of  the  effect  of  color  on  the  landscape  I  made  no  note.  A  sulphurous  glow  in  the  northeastern 
part  of  the  sky  drew  my  attention  in  that  direction  while  I  was  arranging  my  screens,  shortly  after 
the  second  contact.  It  rose  a  few  degrees  above  the  horizon  here,  but  not  so  high  elsewhere.  It  pre- 
sented the  appearance  of  a  sunset  after  a  heavy  thunder-storm  with  the  sun  already  below  the  hori- 
zon, and  illuminating  the  under  edge  of  the  low  hanging  clouds.  The  phenomenon  was  generally 
observetl,  and  produced  a  great  impression  on  all. 

THE  THIRD  CONTACT. 

By  an  unfortunate  substitution  of.  a  deep  red  for  my  ordinary  neutral-tinted  screen,  1  lost  the 
third  contact  by  about  ten  seconds,  supposing  I  was  witnessing  the  sun's  hydrogen  atmosphere,  when 
I  was  observing  his  limb.  Ascertaining  my  mistake  I  called  time,  and  was  given  Gh  3m  45K 
chronometer  time ;  my  cousin  remarking  that  he  could  now  see  to  read  the  second-hand  without  the 
assistance  of  (lie  lights  in  the  window.  I  estimate  12*  to  have  elapsed  from  time  of  third  contact. 

The  receding  limb  of  the  moon  was  less  rough  than  the  eastern  one.  Had  it  given  any  appear- 
ance like  •'  Baily's  Beads"  on  revealing  the  first  line  of  light  from  the  sun's  disk,  I  should  certainly 
have  detected  it,  so  intently  was  I  watching  the  point  at  which  the  sun's  limb  was  to  appear. 

A  reference  to  the  tliermometrical  record  kept  by  Mr.  Farrell  reveals  the  fact  that  the  temper- 
ature of  the  air  fell_from  7(i°  at  first  contact  to  C8°  at  eleven  minutes  after  the  reappearance  of  the 
snn.  This  latter  temperature  was  the  lowest  reached  during  the  eclipse.  One  hour  later  the  ther- 
mometer marked  71°,  and  at  7  p.  in.  it  read  C4°.5. 

THE  LAST  CONTACT. 

The  last  contact  occurred  at  71'  I"1  36s. 

W.  S.  OILMAN,  JK. 
Commodore  B.  F.  SANDS,  IT.  S.  N., 

United  States  Naval  Observatory,  Wnxhinyton. 


182 


REPORT    OF   MR.    W.    S.    OILMAN,    JR. 


A.— METEOROLOGICAL  KECOKD.— IN  LOCAL  TIME. 

AUGUST  5,  1869. 


Hour. 

Therm. 

Sky. 

Wind. 

Clouds. 

Remarks. 

11       A.M. 

o 
79.5 

Overcast     8 

NE. 

Dark  Niuib. 

Shower. 

12       M. 
1        P.M. 
2        P.  M. 

70.5 

73. 
75.7 

Overcast    HI 
Overcast    10 
Overcast     9 

E.NE. 
E. 
SE. 

Lighter  Niuib. 
Lighter  Niiul). 
Stratified. 

Wind  blowing  in  gusts. 

3        P.M. 

78.5 

Clear 

SE. 

Stratified. 

4        P.  M. 

77. 

Clouds          3 

E. 

Stratified. 

5        P.M. 

74.  5 

Clouds          1 

E. 

Stratified. 

6        P.M. 

71. 

Clouds         5 

E. 

Stratified. 

7        P.M. 

ee.7 

Clouds         9 

E. 

Stratified. 

8        P.M. 

68. 

Overcast    10 

E.  by  S. 

AUGUST  (i,  18(>9. 


6      A.  M.          64. 

Overcast    10 

NE. 

Stratified. 

7      A.  M.           63. 

Overcast    10 

NE. 

Stratified. 

Misty  rain. 

8      A.  M.           64.     .        Overcast    10 

N.  NE. 

Stratified. 

Misty  rain. 

0      A.  M.           6-2. 

Overcast    10 

NE.           i  Stratified. 

Misty  rain. 

10      A.  M.           62. 

Overcast    10 

NE. 

Stratified. 

Misty. 

11      A.  M.           64. 

Overcast    10 

NE. 

Clouds  higher. 

Misty. 

12      M.                66. 

Overcast    10 

NE. 

Still  higher. 

Misty. 

1      P.  M.           68. 

Overcast    10 

NE. 

Clouds  higher. 

Misty. 

2      P.M.           71.5 

Overcast     9 

NE. 

Clouds  higher. 

Sun  at  intervals. 

3      P.M.           72.25 

Overcast      9 

NE. 

Clouds  thin. 

4      P.M.           68.5 

Overcast    10 

NE. 

Clouds  thicker. 

5      P.  M.           66.  5 

Overcast    10 

NE. 

Softer  edgi'il. 

6      P.M.           65.5 

Overcast    10 

NE. 

Softer  edged. 

7      P.  M.           65. 

Overcast    10 

NE. 

Softer  edged. 

8      P.  M.           64. 

Overcoat    10 

E. 

Softer  edged. 

AUGUST  7,  1869. 


6       A.M. 

58.5 

Overcast    10 

E. 

7        A.  M. 

60.5 

Overcast    10 

E. 

Thin  overhead  and  in  SE.  —  moving  N. 

8        A.M. 

64. 

Overcast      8 

SE. 

Clouds  thin  —  moving  rapidly  to  NW. 

S)       A.  M. 

68.5 

Overcast    10 

SE. 

Clouds  thicker.                                                                                      » 

10       A.M. 

67. 

Overcast    10 

E.  by  S. 

Clouds  thicker. 

11        A.  M. 

71. 

Overcast    10 

SE. 

Clouds  thinner. 

12       M. 

73.  75 

Thinly  "      9 

SE. 

Sun  visible  at  intervals. 

1        P.  M. 

77. 

Thinly  "      8 

SE. 

Sun  visible  at  intervals. 

2       P.  M. 

75.5 

Thinly  "      5 

SE. 

Snu  visible  at  intervals. 

OBSERVATIONS    OF    THE    ECLIPSE    OP    AUGUST    7,    1869. 


183 


Hour. 

Therm. 

Sky. 

Hour. 

Therm. 

Sky. 

c 

o 

2  30  1'.  M. 

78. 

Clear 

4  35  P.  M. 

68.5 

C'lciir 

:!       r.  M. 

7.">.  r> 

Clear 

4  40  P.  JL 

68.25 

Clear 

3  15  P.  M. 

70. 

Clear 

4  45  P.  M. 

68. 

Clear 

3  30  P.  M. 

7(5. 

Clear 

4  50  P.  M. 

68. 

Clear 

3  45  P.  M. 

76. 

Clear 

4  55  P.  M. 

68.5 

Clear 

4         P.  M. 

«  74.  25 

Clear 

5        P.M. 

69. 

Clear 

4  05  P.M. 

73.  5 

Clear 

5  15  P.  M. 

70. 

Clear 

4  10  P.  M. 

73. 

Clear 

5  30  P.  M. 

71. 

Clear 

4  15  P.  M. 

72. 

Clear 

5  45  P.  M. 

4  20  P.  M. 

71.  5 

Clear 

6        P.  M. 

4  25  P.  M. 

70.  75 

Clear 

6  15  P.  M. 

68.  5 

4  30  P.  M. 

69.  75 

Clear 

6  30  P.  M. 

67. 

4  31  P.  M. 

69. 

Clear 

7         P.  M. 

64.  5 

4  32  P.  M. 

69.    -j  & 

Clear 

4  33  P.  M. 

68.5    | 

Clear 

4  34  P.  M. 

68.  5  J  £ 

Clear 

AUGUST  8,  1869. 


Hour. 

ITier. 

Sky.                Wind. 

Clouds. 

Remarks. 

r 

0 

6        A.  M. 

59. 

Hazy  to  \.         SE. 

7         A.  M. 

04. 

Hazy 

SE. 

8        A.  JI. 

68.  5 

Hazy 

S. 

Clouds  low  on  horizon. 

9        A.  M. 

71.5 

Ila/.y 

S.SE. 

Few  faint  milky  clouds  in  N. 

10        A.  M. 

75.  5 

Cloudy        10 

S. 

Few  faint  milky  clouds  in  N. 

11        A.M. 

76.5 

Cloudy         9 

s. 

Few  faint  milky  clouds  iu  N. 

12        M. 

80.7 

Cloudy         8 

s. 

Cum.  all  over  sky. 

1        P.  M. 

81.5 

Cloudy         8 

S.SE. 

Cum.  all  over  sky. 

2        P.  JI. 

81.  25 

Clear          10 

S.SE. 

Few  Cum.  in  W. 

3        P.  JI. 

81.2! 

Clear           10 

S.SE. 

Few  Cum.  in  SE.  and  SW. 

4        P.M. 

80.  5 

Clear          10 

S.SE. 

Few  Cum.  on  horizon  W.  &  NW. 

5        P.  M. 

77.  5 

Cloudy         6 

SE. 

Very  dark. 

6        P.M. 

75. 

Cloudy        8 

SE. 

Dark  iu  W. 

7  20  P.  JI. 

7:1. 

Clondy 

S.  SE. 

Dark  in  W. 

8        P.M. 

73. 

Cloudy         8 

S.  SE. 

Clouds  thinner  iu  W. 

i 

B. — Comparisons  for  time.     Times  of  contact  and  of  disappearance  and  reappearance  of  sun  spots. 

By  the  courtesy  of  Professors  Newcomb  and  Harkness  I  was  able  to  make  accurate  comparisons 
for  time,  both  before  and  after  the  eclipse,  at  the  temporary  observatory  on  Third  street,  Des 
Moines.  I  had  a  similar  opportunity  at  the  Dearborn  Observatory,  Chicago,  on  the  IGth,  and  finally 
at  the  Naval  Observatory,  Washington,  on  the  occasion  of  presenting  the  foregoing  report  on  the 
20th  of  August  last,  when  I  was  assisted  by  yourself  and  Professor  Yarnall. 

Of  these  comparisons  I  give  below  those  which  I  consider  the  most  reliable. 


184  REPORT    OF    MR.    W.    S.    OILMAN',    JR. 


Des  Moines,  July  31,  1860. 

Hammond  No.  300.  Negus  No.  131!» 

A.      MI.        «.  '<•  '»•        ». 

4    36     14.2p.m.  0  36       0 

Negus  fast  of  Des  Moines  mean  time  6  18  13.  7 

Des  Homes  mean  time  3  17  46.  3 

Longitude  of  temporary  observatory  1  6  16.  09 

Washington  mean  time  -1  2-4       2.  39 

Hammond  fast  of  Washington  mean  time  12  11.  81 

4  36  14.  20 


Des  Moines,  August  12,  1869. 

Hammond  No.  300.  NY-jus  No.  1319. 

//.        Ml.            8.  /'.  W.  x. 

4     18     46. 1p.m.  9  19  0 

Negus  fast  of  Des  Moines  mean  time  6  18  19.5 

Des  Moines  mean  time  3  0  40. 5 

Longitude  of  temporary  observatory  1  6  16. 09 

Washington  mean  time  1  6  56. 59 

Hammond  fast  of  Washington  mean  time  11  49.51 

4  18  46. 1 


[3.] 
Dearborn  Obserratory,  Chiecif/o,  August  16,  1869. 

Hammond  No.  300.  Observatory  mi'iin  lime  dock. 

A.     m.        s.                                                                                                                      ti.  MI.  s. 

4    39    35p.m.                                                                                           3  45  30 

Longitude  west  of  Washington  42  14.26 

Washington  mean  time                                                                             4  27  53.  26 

Hammond  fast  of  Washington  mean  time  11  41.  74 

4  39  35 


In  this  comparison  the  longitudes,  from  Greenwich,  of  Chicago  and  Washington,  are  taken 
respectively  at  5b  50"126S.65  and  51'  8™  12S.39.  These  values  I  obtained  from  Professor  Safford  and 
Professor  Yarnall. 


United  8t<itex  Xarul  Obsei-ratory,  WHxliiiiytnn,  August  20,  1869. 

Hammond  No.  300.  Mi-:in  ti  .....  clock. 

A.     m.        s.  I'-    MI.        s. 

.      3     23    34.5  3     12       0 

Hammond  fast  of  Washington  mean  time  11    34.  5 


3    23    34.5 


OBSERVATIONS    OF   THE    ECLIPSE    OF    AUGUST   7,    1369. 


185 


From  the  above  I  reach  the  following  conclusions  : 


Loss  of  chronometer  Xo.  300,  July  31  to  August  12  = 


Loss  of  chronometer  Xo.  300,  August  12  to  August  16  = 


(1.)  22.3 
(2.)  7.77 
(3.)  7.24 


Loss  of  chronometer  Xo.  300,  August  16  to  August  20  = 

From  the  first  interval  (1.)  we  obtain 

229.3  H-  12  days^=  P.858  loss  per  diem. 
From  the  second  interval  (2.)  we  obtain 

7*.77  4-  4  days  =  19.942  loss  per  diem. 
From  the  third  interval  (3.) 'we.  obtain 

7S.24  4-  3a.95  =  ls.832  loss  per  diem. 

Taking  1s.  86  as  the  daily  rate  at  time  of  eclipse,  and  reckoning  backward  from  August  12  to 
August  7,  I  find  that  my  chronometer  lost  9".5  between  these  dates,  and  therefore  llm  59s  is  the 
amount  to  be  deducted  from  all  the  times  given  in  my  report  to  reduce  them  to  Washington  mean 
time. 

Times  of  Conlaci. 

1st  contact 
2d  contact 
3d  contact 
4th  contact  - 

Probable  duration  of  totality  at  St.  Paul  Junction  2    47s. 

Timed  of  disappearance  and  reappearance  of  sun  spots. 


Chronometer.                     Washington  moan  time. 

k. 

in. 

s. 

ft. 

in. 

s. 

4 

57 

9 

]>.  in. 

4 

45 

10  p.  in. 

6 

0 

45. 

5 

5 

48 

46.5 

6 

3 

33 

(!) 

5 

51 

34  (?) 

7 

1 

36 

6 

49 

37 

Disappearance. 

Group  Xo  1. 
Group  Xo.  2. 
Group  Xo.3. 
Group  Xo-  4. 

Reappearance. 

Group  Xo.  1. 
Group  Xo.  3. 
Group  Xo.  2. 
Group  Xo.  4. 
24* 


Chronometer. 
5    24     10 
5    43    25.5 
5     45    23. 5 
5    58    35 


6  17  58 

6  40  12. 5 

6  44  46 

6  57       4.5 


Washington  mean  time. 
5    12     11 
5    31    26. 5 
5    33    24. 5 
5    46    36 


6  5  59 

6  28  13. 5 

6  32  47 

6  45  5. 5 


REPORT 


OF 


Mil.   F.    W.    B  A  ED  WELL, 


REPORT   OF    MR.  F.  W.  BARDWELL. 


UNITED  STATES  NAVAL  OBSERVATORY, 

Washington,  D.  C.,  September  20,  1869. 

SIR  :  I  have  the  honor  to  submit  the  following  statement,  from  notes  made  at  the  time,  of  the 
results  of  my  observations  of  the  total  eclipse  of  the  sim  on  the  seventh  of  August  last,  in  Bristol, 
Tennessee,  near  the  central  line  of  totality. 

Accompanied  by  Mr.  Thomas  Davidson,  naval  constructor  United  States  ]$avy,  I  arrived  in 
Bristol  on  tin-  day  of  the  eclipse,  at  an  early  hour  in  the  morning,  with  an  interval  of  time  suffi- 
cient to  select  a  suitable  point  for  making  observations. 

I  found  stationed  near  there  a  Coast  Survey  party  with  General  Cutts,  who  kindly  furnished 
me  with  the  latitude  and  longitude  of  their  station,  which  they  had  determined  with  every  facility 
for  accuracy.  1  also  obtained  from  them  a  correction  for  clock  error,  fully  answering  every  desired 
purpose. 

The  point  finally  selected  lor  the  purpose  of  observing  the  eclipse  was  on  the  brow  of  a  hill 
moderately  elevated  above  the  surrounding  country,  with  an  extended  view  of  the  western  horizon, 
at  a  distance  from  the  stations  of  other  parties,  and  far  enough  from  the  public  highway  to  be 
free  from  the  intrusion  of  idle  visitors.  The  elevation  above  tide-water  was  about  sixteen  hundred 
and  eighty  feet,  and  thus  favorable  for  a  clear  state  of  the  atmosphere. 

I  intended  to  give  special  attention  during  the  time  of  total  obscuration  to  the  search  for  an 
intra-mercurial  planet,  and  at  other  times  to  note  any  phenomena  which  would  be  useful  for  com- 
parison with  the  observations  of  others. 

For  the  purpose  of  detecting  the  appearance  of  any  stranger  planet,  1  had  prepared  a  star- 
chart  or  map  showing  the  relative  positions  of  the  line  of  the  ecliptic,  the  apparent  horizon,  the 
Sun,  Mercury,  Venus,  and  the  neighboring  stars  of  not  less  than  the  fifth  magnitude,  within  four 
degrees  on  either  side  of  the  ecliptic,  and  within  ten  degrees  of  the  sun.  I  was  also  provided  with 
a  glass  of  magnifying  power  sufficient  to  show  distinctly  the  spots  on  the  sun's  disk. 

In  using  this  instrument  it  was  merely  strapped  to  a  stake  firmly  driven  into  the  ground,  so 
as  to  secure  steadiness  of  motion  in  directing  it  to  different  portions  of  the  field  to  be  examined. 

During  the  early  part  of  the  day  the  sky  was  partially  overcast,  and  much  anxiety  was  felt 
lest  the  grand  event  should  be  shorn  of  much  of  its  interest;  to  observers  by  the  obscuration  of 
clouds;  but  about  noon  the  sky  became  much  brighter,  and  as  the  critical  hour  approached  it 
seemed  in  the  most  favorable  condition. 

Everything  being  in  readiness,  I  was  prepared  to  observe  the  first  contact  of  the  edge  of  the 
moon  upon  the  sun's  disk.  It  was  arranged  that  I  should  observe  the  instant  of  contact  and  call 
time,  while  Mr.  Davidson,  observing  the  watch  and  counting  seconds,  should  mark  the  time  called. 

The  record  showed  the  time  of  first  contact,  corrected  for  clock  error,  to  be  5h  4m  12s,  mean 
Washington  time,  which  was  sensibly  later  than  was  anticipated.  The  total  obscuration  of  the 
sun  commenced  at  6h  lm  16s,  continued  2m  30s,  and  ended  at  6h2m  468.  During  the  progress  of  the 
eclipse  numerous  notes  of  the  phenomena  were  recorded,  some  of  which  are  here  transcribed  with 
the  corresponding  dates: 

"5h20m. — The  edge  of  the  moon  seems  slightly  serrated  or  rough..  The  disk  of  the  sun  is 
well  defined,  and  shows  eight  spots  in  four  groups. 

"  5h  29m.— Visible  diminution  of  light, 

"5h41m. — Light  dimmed  still  more.  The  line  between  the  shadows  of  clouds  and  the  sunshine 
in  the  valley  below  is  quite  faint. 

"5h55m. — Light  nearly  the  same  as  when  the  sun  is  hid  behind  a  high  hill  just  before  setting." 


190  REPORT    OF    MR.    F.    W.    BARDWELL. 

During  the  time  of  totality  the  positions  of  Venus,  the  Moon,  and  Mercury  appeared  near 
enough  in  a  direct  line  to  guide  me  in  the  brief  search  for  new  planets,  but  none  appeared  in  view. 

Mercury  seemed  to  shine  with  the  full  light  of  a  star  of  the  first  magnitude,  and  Venus  very 
much  brighter,  while  Regulus,  which  is  classed  as  nearly  of  the  first  magnitude,  appeared  scarcely 
as  bright  as  one  of  the  second  class,  but  it  remained  visible  several  seconds  after  the  reappearance 
of  the  sun's  rays.  Almost  immediately  after  the  disappearance  of  the  sun's  disk  a  prominence, 
which  I  described  at  the  time  as  "  a  rosette  of  bright  purple,"  appeared  at  the  edge  of  the  moon 
Avhere  the  sun  had  disappeared ;  then  another  on  the  lower  limb  of  the  moon — that  is,  on  the  edge 
seen  nearest  the  western  horizon ;  and  lastly  appeared  still  another  at  the  point  where  the  sun  was 
about  to  reappear,  while  that  first  seen  had  nearly  or  quite  disappeared.  The  order  in  which  these 
appeared  successively  and  disappeared  showed  that  they  belonged  to  the  sun  and  not  the  moon — a 
point  perhaps  well  enough  established  already.  The  disappearance  of  the  first  of  these  before  the 
reappearance  of  the  suu,  and  the  sensible  interval  of  time  before  the  third  one  made  its  appear- 
ance, showed  that  the  apparent  height  of  these  prominences  (first  and  third  of  those  above 
described)  was  less  than  the  difference  between  the  apparent  diameters  of  the  suu  and  moon. 
With  regard  to  the  second  of  these  prominences — that  is,  the  one  seen  below  the  lower  limb  of  the 
moon — if  it  was  visible  to  observers  near  the  northern  limit  of  the  path  of  totality,  the  inference 
would  be  fair  that  its  apparent  height  was  equal  to  or  greater  than  the  difference  between  the 
apparent  diameters  of  the  sun  and  moon.  If,  on  the  other  hand,  it  was  invisible  at  such  point, 
then  it  would  be  fair  to  infer  that  its  apparent  height  was  less  than  the  difference  of  tin-  apparent 
diameters  of  the  sun  and  moon.  Whether  it  was  indeed  visible  at  any  such  point,  I  am  not 
informed. 

At  my  station,  no  prominences  \vciv  seen  above  any  portion  of  the  moon's  upper  limb,  while 
such  prominences  were  visible  at  other  stations,  which  fact  indicated  that  my  station  was  nearer 
the  southern  limit  of  the  path  of  totality.  There  were  several  indications  that  the  central  line  ol' 
totality  was  further  north  than  the  predicted  place. 

So  far  as  I  have  been  able  to  compare,  it  would  seem  that  the  position  of  these  prominences 
relatively  to  the  sun's  equator  is  within  the  same  limits  of  distance  as  the  spots  on  the  sun's  disk; 
and  it  is  possible  that  some  relation  may  be  found  to  exist  between  the  two  classes  of  phenomena. 

With  regard  to  the  search  for  an  intra-mercurial  planet,  the  evidence  so  far  seems  merely  neg- 
ative, and,  considering  all  the  difficulties  necessarily  attendant  on  the  search,  is  by  no  means  con- 
clusive against  its  existence.  It  is  quite  possible  that  this  interesting  question  will  yet  be  defi- 
nitely settled  by  new  methods  which  were  suggested  while  prosecuting  the  recent  search. 

The  clear  atmosphere  free  from  haziness  gave  the  corona  a  well-defined,  brilliant  appearance, 
and  altogether  the  circumstances  were  extremely  favorable  for  witnessing  this  spectacle  of  beauty. 

The  elevation  of  my  station  above  tide-water,  sixteen  hundred  and  eighty  feet,  was  estimated 
from  the  records  of  the  survey  of  the  Virginia  and  Tennessee  Railway. 

Estimates  of  the  latitude  and  longitude,  as  already  stated,  were  based  on  those  of  the  Coast 
Survey  station : 

Latitude 36°  35'  30"  N. 

Longitude 5      9    0  W. 

Nothing  further  of  importance  is  suggested  by  the  memoranda  of  my  observations. 
Very  respectfully,  your  obedient  servant, 

F.  W.  BAKDWELL,  Aid. 
Commodore  B.  F.  SANDS,  U.  S.  N., 

Superintendent  U.  S.  Naval  Observatory,  Washington,  I),  C. 


REPORT 


BREVET  BRHI.  GEN.  ALBERT  J.  IYER, 

CHIEF   SIGNAL   OFFICER  U.  S.  A. 


REPORT  OF   BREVET   BRIG.  GEN.  ALBERT   J.  MYER, 
CHIEF    SIGNAL    OFFICER  U.  S.  A. 


OFFICE  OF  THE  CHIEF  SIGNAL  OFFICER, 

Washington.  D.  C.,  November  2,  I860. 

COMMODORE:  I  avail  myself  with  pleasure  of  the  invitation  extended  iu  your  courteous  note  of 
the  1st  instant  to  communicate  to  yon  the  details  of  observations  made  by  me,  in  company  with 
Colonel  W.  Wintlirop,  also  of  the  army,  of  the  total  eclipse  of  the  sun  on  August  7,  1809,  from  the 
summit  of  White  Top  Mountain,  near  Abingdon,  Virginia.  Yon  will  please  understand  the  word 
"  observations"  in  its  simplest  colloquial  sense,  our  expedition  having  been  of  the  most  informal  and 
impromptu  character ;  and  our  only  instruments  two  telescopes  (not  reversing)  of  a  magnifying 
power  (measured)  of  about  forty-eight  and  four-tenths  (48.4)  diameters.  With  these  we  used,  for 
solar  observation,  obscuring  glasses  or  screens  of  plain  red  glass,  thicknesses  of  which  were  added 
or  taken  away  as  occasion  required  greater  or  less  obscuration.  The  point  of  observation,  a  mount- 
ain top,  was  sought  with  a  view  of  placing  ourselves  as  far  as  possible  above  the  lower  and  denser 
strata  of  the  atmosphere  and  the  smoke,  ha/e,  and  obstacles  to  vision  with  which  they  are  charged. 
The  extensive  field  of  view  was  also  desirable.  The  ascent  of  the  mountain,  which  lies  in  the  midst 
of  a  wilderness  at  the  junction  of  the  State  lines  of  Virginia,  Tennessee,  and  North  Carolina,  having 
been  effected  after  a  night's  encampment  in  the  woods  and  a  somewhat  severe  inarch,  early  in  the 
day  an  excellent  position  was  selected,  and  the  instruments  were  placed  upon  a  flat  rock  on  the 
open  summit,  from  which  was  had  a  comprehensive  view  for  fifty  (50)  miles,  over  billows  of  mount- 
ains, in  near  and  distant  ranges,  and  across  the  valley  of  the  Holston  to  the  westward. 

During  all  the  morning,  and  until  afternoon,  the  sky  was  wholly  overcast  witli  thin  white 
clouds,  through  which  the  sun's  disk  was  dimly  visible.  At  about  3  o'clock,  however,  a  breeze 
sprang  up  from  the  northward,  which,  in  the  course  of  an  hour,  nearly  cleared  the  western  sky  of 
clouds,  so  that  a  perfectly  unobstructed  view  of  the  eclipse  was  had  from  the  beginning  to  the  end 
of  the  obscuration,  and  with  the  advantage  that  the  effect  of  the  changing  light  upon  the  masses  of 
cloud  near  the  apparent  place  of  the  sun,  and  elsewhere  above  the  horizon,  could  be  noted. 

Upon  first  turning  the  telescopes  upon  the  sun,  the  spots  upon  its  surface  were  noticed  located 
as  appears  in  the  various  photographs  taken  by  other  observers,  which  have  doubtless  been  under 
your  observation.  The  spot  near  the  lower  (southern)  limb  was  the  larger,  and  exhibited,  as  it 
seemed  to  us,  a  remarkably  distinct  penumbra. 

The  first  exterior  contact  was  readily  perceived,  but  no  record  of  time  was  made. 

During  the  progress  of  the  eclipse  it  was  endeavored  to  observe  whether  there  was  change  in 
the  appearance  of  the  spots  on  the  sun  as  they  were  approached  and  then  covered  from  view  by  the 
moon's  disk ;  and  also  whether,  with  glasses  of  the  power  used  by  us,  any  lunar  prominences  could 
be  observed  as  projected  against  the  disk  of  the  sun  as  a  background.  The  lunar  limb  did  not 
exhibit,  to  our  eyes,  a  sharply-defined  or  clear  line,  either  as  against  the  unobscured  sun's  disk  or 
as  covering  the  spots,  but  no  prominences  were  noted.  * 

The  first  strikingly  remarkable  accompaniment  of  the  phenomenon  which  was  observed  was  a 
flight  of  brilliant  particles,  seen  by  Colonel  Winthrop,  my  companion,  and  described  by  him  as  a 
"  shower  of  bright  specks,"  to  which  he  more  than  once  called  my  attention  while  yet  some  four  or 
five  digits  of  the  sun's  disk  remained  uncovered,  and  which  we  do  not  doubt  was  the  shower  of 
meteors  remarked  upon  by  other  observers.  I  was  at  the  time  using  obscuring  glasses  too  dense  to 
permit  the  light  of  these  meteors  to  be  observed,  a  fact  which  has  some  bearing  in  reference  to  other 
observations  made  a  few  moments  later. 

The  next  principal  feature  was  one  which  I  have,  not  perceived  to  have  been  yet  recorded  in  the 
published  reports  of  other  parties.    While  some  two  digits  of  the  sun's  disk  were  still  uueclipsed, 
and  many  seconds,  perhaps  a  minute,  before  any  appearance  of  the  breaking  of  the  visible  sun  cres- 
cent into  Baily's  Beads,  there  was  distinctly  seen  by  both  my  companion  and  myself,  and  verified 
25* 


194  REPORT  OP  BREVET  BRIG.  GENERAL  ALBERT  J.  MYER. 

by  attention  mutually  and  repeatedly  directed  to  it,  a  luminous  cloud  or  prominence  of  a  yellow  line, 
upon  the  lunar  limb  below  the  solar  crescent,  and  removed  about  fifteen  or  twenty  degrees  of  the 
sun's  apparent  circumference  from  its  lower  extremity.  It  appeared  as  if  from  behind  or  attached 
to  the  moon's  disk  (southeastern  portion)  at  this  part  of  its  circumference,  of  course  showing  an  inky 
blackness.  This  object  did  not  appear  to  be  detached  or  floatiTig.  It  was  fixed  in  its  position  and 
distinctly  changed  shape,  either  in  itself  or  by  movement  of  the  moon's  limb  while  under  observa. 
tion.  Its  outlines  were  not  sharp.  An  appearance,  barely  visible,  was  thought  to  be  noticed  at  its 
northern  and  upper  part,  as  might  be  of  a  thinner  portion  of  the  denser  cloud  drifting  northward. 
No  motion  was  perceptible.  The  whole  prominence  was  carefully  observed  for  some  seconds.  It 
must  have  been  of  a  very  considerable  brilliancy  to  have  been  so  distinctly  seen  while  so  much  of 
the  sun's  disk  was  nnobscured,  and  to  have  been  so  plainly  observed  through  the  dense  obscuring 
glasses  then  stilLiu  use.  It  occurred  tons,  and  it  has  been  suggested  by  others,  that  it  might  have 
been  one  of  the  red  or  rose-colored  prominences  afterward  visible  during  the  totality,  and  now  ear- 
lier observed  under  different  circumstances  of  illumination,  &c.  If  this  be  so,  it  would  seem  to 
establish  that  these  protuberances  emit  a  considerable  light ;  the  observed  cloudy  prominence 
appearing  distinctly  luminous,  either  by  its  own,  or  reflected, or  transmitted  light;  and  more  lumi- 
nous at  its  base,  and  near  the  moon's  limb,  than  at  its  apex.  As  I  now  recall  the  eclipse,  some  of 
the  red  protuberances,  and  larger  than  this  appeared,  were  at  the  moment  of  totality  visible  beyond 
the  circumference  of  those  portions  of  the  sun's  disk  yet  unobscured  at  the  time  of  this  observation. 
If  these  prominences  possess  such  brilliancy,  it  would  seem  these  ought,  at  this  time,  to  have  been 
also  visible  through  the  obscuring  glasses.  This  would  particularly  apply  to  the  prominence  after- 
ward noted  at  about  the  center  of  the  eastern  limb,  and  that  near  the  center  of  the  northern  limb. 
Xone  were  in  view.  This  object  did  not  answer  to  the  description  of  a  detached  luminous  point 
noticed  by  M.  Laussedat,  as  observed  at  the  lower  extremity  of  the  sun's  cresent  at  the  total  eclipse 
of  July  18,  18(50.  It  was  further  removed  from  the  crescent,  and  though  exhibiting  through  our 
colored  (red)  glasses  light  of  the  same  appearance  as  that  of  the  sun's  disk,  it  was  not  so  bright  or 
intense.  We  were  much  impressed  with  the  appearance  at  the  time.  Our  limited  experience  did 
not  permit  us  to  account  for  it,  and  I  am  pleased  to  be  able  to  submit  the  subject  for  more  compe- 
tent consideration. 

Upon  the  breaking  of  the  sun's  crescent  into  the  Baily's  Beads,  the  crescent  seemed  to  divide 
at  first,  at  about  the  center,  into  two  separate  masses,  each  of  which  immediately  parted  into 
numerous  fragments  and  then  disappeared.  At  the  moment  of  totality  we  ceased  to  use  screens  or 
obscuring  glasses  of  any  kind  with  the  telescopes.  Colonel  Winthrop  had  been  using  hut  a  slight 
screen  only  for  some  moments  before.  The  red  prominences  were  at  once  visible. 

The  telescopic  appearance  of  the  corona  or  aureola,  during  the  totality,  exhibited  a  clear,  yel- 
lowish bright  light  closely  surrounding  the  lunar  disk  and  fading  gradually,  with  perhaps  some 
tinge  of  pinkish  green,  into  the  hue  of  the  darkened  sky.  Upon  this  corona,  extending  beyond  its 
brightest  portion,  the  well  defined  rose-colored  prominences  were  projected  at  various  points  of  the 
circumference.  They  were  larger  in  appearance  and  more  distinct  than  we  had  been  led  to  expect 
from  such  illustrations  of  total  eclipses  as  we  had  seen.  We  observed  no  rose-colored  clouds  or 
objects  appearing  as  detached  from  the  sun's  circumference,  or  as  if  floating  in  an  atmosphere. 
Those  visible  to  us  gave  the  impression  of  attachment  to  the  sun  by  their  bases.  They  were  of 
irregular  conical  shape.  They  showed  steadily  without  any  waving  or  flickering  as  of  moving  llame. 
and  presented  sharp  outlines  and  an  appearance  suggestive  at  the  time  of  their  consisting  of 
straight  red  rays  something  like  such  as  are  seen  in  the  jet  of  flame  springing  from  an  ignited 
red  light — a  pyrotechnic  composition  compressed  in  a  tubular  case.  The  exception  to  this  steadi- 
ness was  noted  in  the  instances  of  the  two  central  prominences  of  a  number  of  four,  observed  a  few 
instants  only,  on  the  western  limb  of  the  sun  at  the  time  the  moon's  disk  was  ceasing  to  obscure  it. 
and  almost  simultaneously  with  the  formation  of  the  Baily's  Beads  upon  this  (western)  limb  at  the 
moment  of  emersion.  These  seemed  to  incline,  toward  each  other,  and  to  leap  for  an  instant  into 
view  as  tongues  of  flame  might  do,  and  then  were  invisible  at  once.  They  were  so  instantly  lost  in 
the  light  of  the  unobscured  sun  that  it  could  not  be  determined  whether  this  was  an  actual  motion 
or  an  optical  effect,  caused  by  the  prominence's  being  visible  but  for  an  instant  and  then  disappear- 
ing. The  instan taneousness  with  which  these  red  prominences  disappeared  at  the  moment  of  emer- 


OBSERVATIONS    OF   THE   ECLIPSE    OF   AUGUST   7,  1869.  195 

sioii  would  seem  to  show  that  the  object  first  noted  by  us,  before  the  totality,  must  have  differed 
from  them  in  something  of  composition  or  illumination. 

Of  the  red  prominences,  as  now  recollected,  there  were  visible  seven.  One,  and  the  largest, 
near  the  center  of  the  lower  (southern)  limb,  and  one  near  the  center  of  the  eastern  limb,  were  care- 
fully observed.  One  a  little  to  the  eastward  of  the  center  of  the  northern  limb  was  noticed.  Four 
were  visible,  for  two  or  three  seconds  only,  upon  the  western  limb.  That  near  the  center  of  the  lower 
limb  was  the  larger  and  most  attractive.  Its  size  and  position  have  suggested  that  it  might  be  in 
some  relation  to  the  larger  and  lower  spot  upon  the  sun.  All  the  prominences  were  similar  and 
constant  in  hue,  of  a  deep  rose-color. 

To  the  unaided  eye  the  eclipse  presented,  during  the  total  obscuration,  a  vision  magnificent 
beyond  description.  As  a  center  stood  the  full  and  intensely  black  disk  of  the  moon,  surrounded  by 
the  aureola  of  a  soft  bright  light,  through  which  shot  out  as  if  from  the  circumference  of  the  moon 
straight  massive  silvery  rays,  seeming  distinct  and  separate  from  each  other,  to  a  distance  of  two 
or  three  diameters  of  the  lunar  disk;  the  whole  spectacle  showing  as  upon  a  background  of  diffused 
rose-colored  light.  This  light  was  most  intense  and  extended  furthest  at  about  the  center  of  the 
lower  limb,  the  position  of  the  southern  prominence.  The  silvery  rays  were  longest  and  most  prom- 
inent at  four  points  of  the  circumference,  two  upon  the  upper  and  two  upon  the  lower  portion,  appa- 
rently equidistant  from  each  other,  and  at  about  the  junctions  of  the  quadrants,  designated  as 
"  limbs,"  giving  the  spectacle  a  quadrilateral  shape.  The  angles  of  the  quadrangle  were  about  oppo- 
site the  northeastern,  northwestern,  southeastern  and  southwestern  points  of  the  disk.  A  banding 
of  the  rays,  in  some  respects  similar,  has  been  noted  as  seen  at  the  total  eclipse  of  July  18,  1860. 
There  was  no  motion  of  the  rays;  they  seemed  concentric.  These  discrete  rays  were  not  visible  to 
me,  or  did  not  attract  my  attention  with  the  telescope,  and  the  diffused  rose-colored  light  seemed 
to  resolve  itself  in  the  field  of  the  glass  into  the  prominences.  The  field  of  the  glass,  with  the  whole 
disk  in  view,  did  not  extend  far  beyond  the  prominences.  My  impression  at  the  time  was  that  the 
appearance  of  rays  was  due  to  some  optical  effect.  The  sight  presented  to  the  unaided  eye  was  the 
superior  in  beauty;  that  through  the  glass  in  interest.  This  was  so  markedly  the  case  that  there 
was  a  sense  of  disappointment,  on  resorting  to  the  telescope,  at  finding  the  size  and  beauty  of  the 
spectacle,  as  seen  by  the  naked  eye,  so  much  reduced  by  the  definition  of  the  glass. 

The  approach  of  the  moon's  shadow  did  not  appear  to  be  marked  by  any  defined  line,  or  the 
movement  of  any  dark  column  of  shade  through  the  air.  The  darkness  fell  gradually,  shrouding 
the  mountain  ranges  and  the  dim  world  below  in  most  impressive  gloom.  Our  guides  had  been 
instructed  to  watch  for  the  shadow  as  described,  and  to  call  to  us  at  the  glasses.  They  saw  nothing 
of  which  to  give  notice.  At  the  same  time,  and  in  vivid  contrast,  the  clouds  above  the  horizon 
were  illuminated  with  a  soft  radiance;  those  towards  the  east  with  lights  like  those  of  a  coming 
dawn,  orange  and  rose  prevailing;  those  northward  and  westward,  as  described  to  us  by  Mr. 
Charles  Coale,  of  Abingdon,  Virginia,  who  was  present,  with  rainbow  bands  of  light  of  varied  hues. 
I  quote,  in  his  words,  a  description  written  by  him,  as  of  interest,  in  reference  to  the  dispersion  of 
light:  "  But  the  grandest  of  all  to  us,  who  had  no  astronomical  ambition  or  astronomical  knowledge 
to  gratify,  was  the  effect  upon  the  clouds  during  the  total  obscuration.  Those  who  have  had  the 
privilege  of  being  upon  White  Top,  and  enjoying  the  westward  scene,  will  remember  the  grand 
panoramic  view  of  mountains  beginning  on  the  northern  and  southern  horizon,  and  stretching  away 
to  the  west  till  they  seem  to  meet,  will  appreciate  the  scene  that  we  now  attempt  to  describe. 
Stretching  along  this  semi-circle  of  mountains,  in  long  horizontal  lines,  far  below  the  sun,  lay  light 
and  fleecy  clouds  as  if  resting  upon  their  wings  during  the  seeming  struggle  between  the  orbs  above 
them.  At  the  moment  of  the  falling  of  the  dark  shadow,  when  naught  was  to  be  seen  above  but 
the  stars  and  the  circle  of  light  around  the  moon,  these  clouds  became  arrayed  in  all  colors  of  the 
rainbow,  presenting  an  indescribable  richness,  with  their  background  of  somber  mountain.  To  our 
vision  it  was  as  if  bands  of  broad  ribbon  of  every  conceivable  hue  had  been  stretched  in  parallel 
lines  half  round  the  universe/'  Our  faces  were  not  turned  toward  these,  and  we  did  not  see  them. 
No  rainbow  hues  were  seen  before  or  after  the  eclipse. 

A  very  cursory  examination  only  could  be  given  the  stars  and  planets  visible  during  the  totality, 
as  in  a  clear  twilight  at  evening.  Venus  and  Mercury,  near  the  apparent  place  of  the  sun,  exhib- 
ited an  unexpected  brilliancy.  Colonel  Wiuthrop  was  impressed  with  the  number  of  stars  visible 


196  REPORT  OF  BREVET  BRIG.  GENERAL  ALBERT  J.  MYER. 

here  and  elsewhere  in  the  heavens,  and  not  confined  to  those  of  the  first  magnitude  only,  as  by  far 
greater  than  he  had  been  led  to  anticipate  by  descriptions  of  previous  eclipses. 

The  fall  of  the  temperature,  already  low  at  our  elevation,  was  marked  as  the  obscuration 
approached  and  reached  totality.    Our  horses  continued  to  feed  quietly  during  the  increasing  dark 
ness,  as  at  an  approaching  sunset. 

At  the  moment  of  emersion  the  first  rays  of  the  sun  showed  themselves  at  several  detached 
points  on  its  western  limb,  forming  again  the  Baily's  Beads,  which  united  in  a  delicate  crescent. 

It  was  a  striking  circumstance  connected  with  the  whole  phenomenon  that  so  many  of  its 
details  could  be  observed  with  the  unaided  eye.  In  this  manner  our  guides  saw  very  readily  Bai- 
ly's Beads,  exclaiming  that  the  sun  was  "breaking  to  pieces,"  and  could  distinguish  without  diffi- 
culty some  of  the  protuberances.  Much  was  no  doubt  due  to  the  clearness  of  the  atmosphere  at  so 
great  an  elevation.  White  Top  Mountain  has  been  measured  by  Professor  Guyot,  of  JYinceton 
College,  and  found  to  be  five  thousand  five  hundred  and  thirty  (5,530)  feet  above  the  level  of  the 
sea.  He  states  it  to  be  the  highest  mountain  in  Virginia,  unless  possibly  its  neighbor,  Balsoni 
Mountain,  which,  however,  is  wooded  to  the  summit,  and  would  have  been  unstated  to  our  purpose. 

If  any  interest  can  be  attached  to  this  informal  narration,  it  will  be  because  our  party  was  one  of 
the  very  few,  possibly  the  only  one,  that  observed  successfully  from  a  mountain  top  so  elevated.    It  is 
to  be  regretted  that  the  position  was  not  occupied  by  observers  better  equipped  and  better  qualified. 
I  am,  Commodore,  very  respectfully,  your  obedient  servant, 

ALBERT  ,1.  MYER, 
Brevet  Brigadier  General  and  Chief  /Signal  Officer  of  the  Ann;/. 

Commodore  B.  F.  SANDS,  U.  S.  N., 

Superintendent  United  States  Naval  Observatory,  Washington,  D.  C. 


OFFICE  OF  THE  CHIEF  SIGNAL  OFFICER, 

Washington,  D.  C.,  December  4,  1869. 

COMMODORE:  I  have  the  honor  to  transmit  to  you  an  extract  from  a  letter  just  received  from 
Mr.  Charles  B.  Coale,  of  Abingdou,  Virginia,  in  reply  to  a  communication  in  which  I  requested 
more  specific  information  in  regard  to  the  "rainbow  hues"  observed  by  him  during  the  total  eclipse 
of  August  7,  1869,  and  to  which  reference  was  made  in  my  report. 

I  am,  Commodore,  very  respectfully,  your  obedient  servant, 

ALBERT  J.  MYER, 

Brevet  Brigadier  General  and  Chief  Signal  Officer  of  the  Army. 
Commodore  B.  F.  SANDS,  U.  S.  N., 

Superintendent  U.  S.  Naval  Observatory,  Washington,  1).  C. 


ABINGDON,  VIRGINIA,  November  24, 1869. 

DEAR  GENERAL  :  I  have  been  absent  from  home  seven  weeks. 

In  giving  to  the  clouds  "all  the  colors  of  the  rainbow,"  I  was  probably  bordering  on  the 
extravagant,  though  not  more  so  than  is  allowable  in  country  journalism.  I  distinctly  remember, 
however,  that  there  were  distinct  bands  of  pink,  purple,  yellow,  orange,  and  fiery  red,  and  each 
slightly  tinged  with  different  shades  of  its  own  color.  One  of  the  bands,  I  remember,  had,  to  my 
vision,  a  slight  lilac  tinge.  I  do  not  remember  to  have  observed  any  green  or  blue,  but  1  do 
remember  that  the  lower  edge  of  the  purple  had  a  very  faint  blue  tinge.  All  these  resting  against 
a  dark  background  gave  them  an  indescribably  gorgeous  appearance — the  lines  of  color  seeming  to 
be  divided  by  strips  of  black.  They  all  lay  in  horizontal  lines,  one  above  the  other.  My  impression 
is  that  these  colors  appeared  at  the  moment  the  shadow  passed  from  the  lower  edge  of  the  sun, 
though  I  am  not  positive. 

Having  no  astronomical  knowledge  or  aspirations,  and  no  instrument,  my  whole  attention  was 
directed  to  the  clouds,  and  my  whole  soul  absorbed  in  their  indescribable  grandeur.  * 

Yours,  very  respectfully,  CHS.  B.  COALE. 

General  ALBERT  J.  MYER,  TJ.  S.  A.,  Washington,  D.  C. 


REPORT 


PROFESSOE  ASAPH  HALL,  TJ.  S.  N, 


REPORT   OF   PROFESSOR   ASAPH   HALL,   U.   S. 


UNITED  STATES  NAVAL  OBSERVATORY, 

Washington,  December  7,  1869. 

SIR:  In  accordance  with  thft  order  of  the  honorable  Secretary  of  the  Navy,  dated  May  3,  1869, 
I  proceeded  to  New  York,  and  having  been  joined  there  by  Mr.  Joseph  A.  Rogers,  we  took  passage 
for  San  Francisco  on  the  steamship  of  the  21st  of  May.  At  the  request  of  Paymaster  Eldridge, 
United  States  Navy,  the  officers  of  the  Pacific  Mail  Steamship  Company  and  of  the  Panama  rail- 
road gave  me  letters  of  introduction  to  Captain  Conner  and  to  Captain  Parker,  of  the  steamships 
Henry  Channcey  and  Colorado,  and  to  the  agents  of  the  companies  on  the  isthmus.  To  all  these 
gentlemen  we  are  indebted  for  good  accommodations  for  the  transportation  of  our  chronometers 
and  instruments  and  for  a  safe  and  pleasant  journey.  We  reached  San  Francisco  June  12,  and  the 
same  day  reported  to  Admiral  Craven,  at  Mare  Island  navy  yard.  To  Admiral  Craven  and  the 
officers  of  the  navy  yard,  and  particularly  to  Captain  Phelps,  we  are  indebted  for  every  assistance 
they  could  render  us. 

Lieutenant  Commander  B.  C.  Merrhnan,  in  charge  of  the  Navigation  Office,  furnished  us  with 
seven  chronometers,  a  chronometer-case,  and  a  barometer,  for  the  expedition.  After  making  obser- 
vations at  Mare  Island  to  determine  the  errors  and  approximate  rates  of  the  chronometers,  on  June 
21  we  went  on  board  the  United  States  steamer  Mohican,  Captain  S.  It.  Franklin  commanding,  then 
lying  in  the  harbor  of  San  Francisco.  We  spent  June  23  and  24  in  making  magnetic  observations 
on  the  Island  Ycrha  Buena,  and  on  June  29  the  Mohican  sailed  for  Plover  Bay.  This  bay  is  011  the 
northeastern  coast  of  Siberia,  in  north  latitude  64°  20',  and  in  longitude  61'  2om  west  of  Washington. 
The  following  reasons  led  to  the  selection  of  this  place  for  observing  the  eclipse:  the  computed  line 
of  central  eclipse  passed  only  six  or  eight  miles  off  the  coast;  an  excellent  harbor,  easy  of  access, 
furnishes  a  secure  anchorage  for  all  kinds  of  vessels;  and,  from  all  the  information  I  could  obtain, 
the  chance  of  having  good  weather  is  better  there  than  on  the  American  coast,  and  as  good  as  at 
any  point  in  those  regions,  near  the  line  of  central  eclipse,  that  the  short  time  remaining  for  the 
voyage  would  permit  us  to  reach.  Mr.  William  H.  Ball,  of  the  Smithsonian  Institution,  furnished 
me  witli  a  map  of  Plover  Bay  and  information  concerning  the  natives  of  the  country.  We  reached 
Plover  Bay  July  30,  the  vessel  stopping  on  the  way  at  Nanaimo,  Vancouver  Island,  and  at  Una- 
laska.  The  next  day  Mr.  Rogers  and  I  ascended  the  mountains  on  the  east  side  of  the  bay,  hoping 
to  find  a  suitable  place  for  our  observatory,  but  considering  the  difficulty  and  danger  of  carrying 
the  instruments  up  and  down  the  steep  mountain  trails  and  the  necessity  of  frequently  comparing 
the  chronometers  on  the  ship,  we  decided  to  locate  our  observatory  on  the  sand  spit  at  the  lower 
anchorage.  This  enabled  us  immediately  to  begin  observations  for  time  and  latitude,  and  to  finish 
our  magnetic  observations  before  the  day  of  the  eclipse.  On  August  1  Mr.  Carter,  the  carpenter 
of  the  Mohican,  put  up  our  observatory  on  the  sand  spit,  and  our  instruments  and  bedding  were 
transferred  from  the  ship  in  Emma  Harbor  to  the  observatory,  a  distance  of  about  six  miles.  On 
unpacking  the  instruments  we  found  them  in  good  order,  not  one  having  been  broken  or  injured  on 
the  voyage. 

We  left  Plover  Bay  at  midnight,  August  7,  and  reached  San  Francisco  September  21,  stopping, 
on  our  return,  at  Esquimalt,  Vancouver  Island. 

To  Captain  S.  R.  Franklin,  United  States  Navy,  and  to  the  officers  and  men  of  the  Mohican,  we 
are  indebted  for  the  successful  termination  of  this  long  and  difficult  voyage,  and  we  offer  them  our 
hearty  thanks  for  their  uniform  kindness  to  us. 


200 


REPORT  OF  PROFESSOR  HALL. 


THE  ECLIPSE. 

The  subjoined  sketch  of  the  country  around  Plover  Bay  shows  the  positions  of  our  observing 

stations  and  of  the  ship  in  Emma 
Harbor.  We  thought  it  best  to 
observe  the  eclipse  from  different 
stations,  hoping  that,  in  case  of 
cloudy  weather,  some  of  the  ob- 
servers might  in  this  way  obtain 
observations.  In  order  to  ascer- 
tain if  it  were  practicable  to  take 
instruments  to  the  top  of  the 
mountains  near  the  coast,  on  Au- 
gust 5  Mr.  Eogers,  accompanied 
by  Mr.  liichard  Baker,  made  an 
excursion  from  the  ship  down  the 
valley  to  Lake  Moore.  They  as- 
cended Bald  Head  and  went  down 
the  west  side  of  the  mountain  to 
Plover  Bay.  I  am  indebted  to 
Captain  P.  S.  Itedfield,  of  the 
whaling  brig  Victoria,  of  San 
Francisco,  who  furnished  me  with 
a  five-oared  whale-boat,  a  crew  of 
five  Indians,  and  Mr.  W.  E.  AVhite 
as  boat-steerer.  On  the  evening 
of  August  6  I  went  in  this  boat  to 
the  Indian  village  on  East  Head, 
remained  there  over  night,  and  in 
the  morning  ascended  Bald  Head,  accompanied  by  Mr.  White  and  ten  Indians,  who  carried  the 
instruments.  This  mountain  is  the  second  peak  from  the  sea,  and  is  very  nearly  in  the  meridian 
of  our  observatory  on  the  sand  spit,  and  about  three  miles  south  of  the  observatory. 

During  the  night  of  August  0  the  sky  was  perfectly  clear,  and  a  cool  wind  from  the  north 
promised  a  continuance  of  good  weather.  About  an  hour  before  the  beginning  of  the  eclipse  low 
cumulus  clouds  drifted  rapidly  from  the  west  over  the  sky.  As  the  clouds  passed  toward  the  east 
the  partial  eclipse  was  occasionally  seen  through  the  openings.  On  the  approach  of  the  total 
eclipse  everything  became  hushed  and  still:  the  sea-birds  stopped  their  Mights  and  the  Indians 
huddled  together  in  awe.  As  the  shadow  passed  over  the  mountain  the  effect  was  startling.  In 
the  stillness  and  darkness  of  the  moment  it  seemed  as  though  all  life  had  been  swept  from  the 
earth.  The  fearful  gloom  of  total  eclipse  was  increased  by  the  desolate  appearance  of  the  country, 
without  tree  or  shrub,  or  anything  pleasant  to  the  eye.  Near  the  horizon  a  belt  of  clear  sky,  fifteen 
or  twenty  degrees  in  altitude,  became  of  a  ruddy  color,  like  the  evening  sky  after  sunset  in  autumn. 
At  the  same  time  the  lower  portions  of  the  clouds  toward  the  north  and  east  were  of  a  dull  white 
or  ashy  appearance.  I  could  see  nothing  of  the  protuberances,  and  had  only  at  times  an  indistinct 
view  of  the  corona.  During  the  totality  I  was  able  to  read  the  face  of  my  chronometer  without  the 
aid  of  the  lamp.  The  clouds  were  apparently  denser  toward  the  sea-coast,  and  prevented  me  from 
obtaining  accurate  observations  of  the  times  of  contacts.  Within  an  hour  after  the  end  of  the 
eclipse  the  clouds  had  entirely. disappeared,  and  all  that  long  afternoon  the  sky  was  cloudless. 
The  times  that  I  observed  are  the  following: 

/;.     in.     a. 

Beginning  of  total  eclipse  4      5      0    uncertain, 

End  of  total  eclipse  49    —    very  doubtful, 


with  pocket  chronometer  Dent  7986. 
the  power  employed  was  42. 


The  telescope  used  by  me  has  an  aperture  of  3£  inches,  and 


1869.  201 

The  following  are  the  accounts  of  Mr.  Eogers  and  Mr.  Very,  who  observed  on  the  sand  spit  in 
Plover  Bay : 

DESCRIPTION  OF  THE  ECLIPSE  BY  MR.  ROGERS. 

"The  night  before  the  eclipse  was  perfectly  clear,  and  I  continued  to  make  observations  for 
time  during  the  whole  of  the  short  period  in  which  stars  were  visible  with  the  small  telescope  of 
the  portable  transit.  An  hour  or  two  before  the  beginning  of  the  eclipse  clouds  appeared  in  the 
northwest,  and  rising  rapidly  soon  obscured  the  sun.  About  this  time  Mr.  S.  W.  Very,  navigator 
of  the  Mohican,  arrived  from  the  ship,  bringing  M.  T.  chronometer  Negus  1097,  from  which  the 
times  recorded  below  were  taken.  The  observations  were  made  at  the  observatory  on  the  spit, 
with  the  telescope  loaned  by  the  University  of  Pennsylvania.  The  smaller  telescope  belonging  to 
the  United  States  Naval  Observatory,  and  sidereal  chronometer  Negus  1276,  were  used  by  Mr. 
Very  a  few  yards  distant  from  my  position. 

"  At  the  predicted  time  of  first  contact  the  greater  part  of  the  sky  was  covered  with  clouds,  and 
the  experience  of  the  preceding  week  gave  little  reason  to  hope  that  they  would  be  soon  dispersed. 
They  were  not  quite  continuous,  however,  nor  dense  enough  to  prevent  the  sun's  position  from  being- 
pretty  plainly  indicated  even  when  it  was  quite  invisible. 

"  When  first  seen  through  one  of  the  openings,  the  moon's  limb  had  already  covered  a  consider- 
able portion  of  its  disk.  It  was  several  times  visible  for  a  few  seconds  during  the  partial  phase,  but 
some  time  was  necessarily  lost  in  bringing  it  into  the  field  of  the  telescope,  and  I  was  unable  to 
note  the  occultation  of  any  of  the  spots.  As  the  time  of  total  phase  approached  the  light  gradu- 
ally diminished.  The  sun  appeared  for  an  instant  through  the  clouds  as  a  slender  wire-like  crescent; 
and  a  few  seconds  later  its  obscuration  was  evidently  complete.  Except  a  slight  moaning  of  the 
•wind  at  intervals,  there  was  no  sound  but  that  of  the  sea  on  the  beach  and  the  beat  of  the  chro- 
nometer; and  the  silence  and  gloom  strongly  resembled  that  which  sometimes  precedes  a  thunder- 
storm. The  sky  in  the  southwest  above  the  sea  horizon  was  of  a  deep  orange  color,  while  in  all 
other  directions  the  outlines  of  the  mountains  surrounding  the  bay  were  just  discernible. 

"The  darkness  was  not  so  intense  as  I  had  anticipated ;  but  there  was  apparently  much  less  light 
than  the  twilight  of  the  preceding  midnight.  I  had  taken  the  precaution  to  illuminate  the  face  of 
my  chronometer  by  artificial  light,  and  thought  it  would  not  have  been  possible  to  distinguish  the 
numerals  on  the  dial  without  it.  The  progressive  diminution  of  light  appeared  to  cease  at  9h  17m 
30s;  and  at  9h  20m  0s  a  rapid  increase  of  light  began.  This  interval  is  less  than  the  duration  of 
total  phase,  and  seems  to  indicate  a  very  plainly  perceptible  variation  of  the  illumination  during 
totality;  though  it  may  have  been  partly  owing  to  changes  in  the  density  of  the  clouds. 

"  At  9'1 21™  0s  the  clouds  parted  for  a  few  moments  and  showed  the  emerging  limb  of  the  sun  as 

a  narrow  crescent.  Toward  the  end  of  the  eclipse  it  was  again 
visible  for  a  short  time,  during  which  I  observed  the  complete 
emersion  of  the  umbra  of  a  large  spot  near  the  eastern  limb  at 
10h  23"'  0".r>.  The  apparent  position  of  this  spot,  as  seen  with 
the  telescope  at  llh  Om,  is  shown  at  S  in  the  annexed  diagram. 
At  10h  20"'  57S.5  another  glimpse  of  the  disk  was  obtained,  which 
then  presented  an  unbroken  circular  outline. 

"  The  thermometer  in  the  early  part  of  the  eclipse  had  indicated 
46°  Fahrenheit.  During  total  obscuration  it  fell  to  42°,  and 
afterward  rose  gradually  to  60°  at  the  end  of  the  eclipse.  These 
temperatures  were  noted  by  Mr.  R.  Barker,  captain's  clerk  of  the 
Mohican. 

,  "  The  clouds  which  had  already  begun  to  disperse  soon  disap- 

APPEARANCE  OF  THE  SPOT  AT  1 1  '  o  "    peared  entirely,  and  the  remainder  of  the  day  was  clear  and  warm. 

"JOSEPH  A.  ROGERS." 
26* 


202  REPORT    OF   PROFESSOR   HALL. 

ME.  VERY'S  LETTEE. 

"  UNITED  STATES  STEAMER  MOHICAN,  (third  rate,) 

"  Off  Cape  Tchukotski,  Siberia,  Ai«ji<xt  8,  1869. 

"  SIR  :  I  was  unable  to  make  auy  accurate  observations  of  the  total  eclipse  of  the  7th  iustiint. 
The  times  of  first  contact  and  total  phase  were  lost  on  account  of  the  clouds,  but  the  time  of  egress 
I  obtained  within  two  seconds  after  it  occurred.  By  chronometer  Negus  1276,  (sidereal,)  it  was 
2h  28™  41s. 

"  The  following  are  the  comparisons  made  during  the  day  : 
"  About  5  a.  in.,  before  leaving  the  ship — 

"  Chronometer  Negus  1316,  (standard,)    4h  49™  308.0— 50™  008.0— 50™  30s.O     (Mean  time.) 

"  Chronometer  Negus  1097,  4h  50m  238.5— -50™  538.5— 51™  238.5     (Mean  time.) 

"  About  8  a.  in.  before  observing — 

"  Chronometer  Negus  1097,  7h  41™  008.0— 43m  308-0  (Mean  time.) 

"  Chronometer  Negus  1276,  llh  43™  528.5— 46m  238.0  (Sidereal.) 

"  About  11  a.  m.  after  observing — 

"  Chronometer  Negus  1097,  10h  30™  09S.5— 33m  098.0  (Mean  time.) 

"  Chronometer  Negus  1276,  2h 33™  30s.O—  36™  30s.O  (Sidereal.) 

"  Very  respectfully, 

"SAMUEL  W.  VEEY, 

"Master  and  Navigator.'" 

The  telescope  used  by  Mr.  Very  has  an  aperture  of  2|  inches. 

I  am  indebted  to  Captain  Franklin  for  the  following  account  of  the  eclipse  se'en  from  the  ship 
in  Emma  Harbor : 

"  UNITED  STATES  STEAMER  MOHICAN,  (third  rate,) 

"  Plover  Bay,  Siberia,  August  7,  1869. 

"DEAR  SIR:  As  you  expressed  a  desire  to  get  all  the  information  possible  in  connection  witli 
the  eclipse  of  the  7th  of  August,  and  wished  me  to  give  you  the  benefit  of  what  came  under  my 
observation  at  the  time,  it  gives  me  much  pleasure  to  furnish  you  with  a  copy  of  a  few  notes  I 
then  made. 

"The  eclipse  commenced  about  8.40  a.  m.,  local  mean  time,  on  the  right  upper  edge  of  the  sun  ; 
and  although  the  weather  was  cloudy,  we  were  enabled  from  time  to  time  to  get  a  glimpse  of  it 
through  the  openings  in  the  clouds,  and  thus  mark  its  course  as  it  advanced. 

"  At  about  9.45  the  darkness  became  very  apparent,  and  before  the  sun  was  entirely  obscured 
the  sea  birds  around  us  had  gone  to  roost.  The  darkness  came  upon  us  very  suddenly,  the  clouds 
opposite  the  sun,  from  having  been  a  light  ashy  color,  became  suddenly  black  as  the  blackest  storm 
clouds;  those  under  the  sun  and  in  the  direction  of  the  Arctic  Sea  assumed  a  whitish  hue,  which 
might  have  been  produced  by  the  reflection  from  the  snow  and  ice  of  that  region,  while  those  to 
seaward  took  up  an  orange  and  yellowish  tint.  The  sea  assumed  the  color  of  the  deepest  indigo, 
and  the  whole  scene,  in  its  effects  upon  the  sky,  and  sea,  and  surrounding  hills,  was  sublime  beyond 
anything  of  which  I  can  convey  an  idea ;  nothing  could  present  to  the  mind  a  picture  of  more 
utter  desolation.  There  was  but  one  star*  visible,  owing  to  the  overcast  condition  of  the  sky.  The 
flames  of  the  sun  were  distinctly  visible,  and  three  fiery  lumps  could  be  observed  on  the  edge  of 
the  moon  during  the  totality,  resembling  molten  iron.  The  darkness,  which  continued  for  a  few 
moments,  was  not  complete,  and  passed  away  as  suddenly  as  it  came,  indeed,  it  seemed  to  me  that 
the  transition  from  darkness  to  light  was  more  rapid  than  that  from  light  to  darkness.  Soon  every 
thing  resumed  the  appearance  it  had  before  the  totality,  and  the  eclipse  finished  at  10b  27™  45s  by 
standard  chronometer. 

"  I  am,  very  respectfully,  your  obedient  servant, 

"S.  E.  FRANKLIN, 
"  Commander  United  States  Navy. 

"Professor  ASAPH  HALL,  United  States  Navy." 

"Mercury. — A.  II. 


OBSERVATIONS    OF   THE    ECLIPSE    OF   AUGUST   7,    1869. 


203 


At  the  ship,  Mr.  Inch,  chief  engineer  of  the  Mohican,  and  Mr.  Wainwright,  ensign  United 
States  Navy,  observed  the  times  of  beginning  and  end  of  the  total  eclipse,  but  unfortunately  their 
notes  and  comparisons  with  our  chronometer  were  lost.  Their  observed  duration  of  totality  was 
3'"  0s. 

Collecting  the  times  observed  and  applying  the  correction  of  the  chronometers,  we  have  the 
following  results : 


Station. 

Phase. 

Chronometer. 

Obs.  Time. 

Corr.  Chron. 

Local  M.  T. 

Notes. 

Obs'r. 

. 

h.  m.     s. 

h.  m.     s. 

h.  m.     s. 

Bald  Head  .     .     . 

Bog.  totality 

Dent  7986    . 

450. 

-    6  21  15.  0 

21  43  45.0 

Uncertain    . 

H. 

Sand  Spit    .     .     . 

Beg.  totality 

Negus  1097  . 

9  17  30. 

—  11  32  49.  3 

21  44  40.  7 

Uncertain    . 

R. 

Sand  Spit     .     .     . 

Spot  .     .     . 

Negus  1097  . 

10  23    fr.  5 

—  11  32  49.  3 

22  50  11.  5 

Good       .     . 

R. 

Sand  Spit     .     .     . 

.   "  . 

Negus  1097  . 

10  26  57.  5 

-  11  32  49.3 

22  54    8.2 

.     .     .     . 

E. 

Sand  Spit    . 

Last  contact 

Negus  1276  . 

2  28  41. 

—    6  30  15.  3 

22  52  32.  0 

.     .     .     . 

V. 

Ship              .     .     . 

Last  contact 

Negus  1316  . 

10  27  45. 

—  11  30  55.8 

22  56  49.2 

F. 

Iii  making  these  reductions  I  have  assumed  that  Bald  Head  is  in  the  meridian  of  the  observa- 
tory on  the  sand  spit,  and  that  the  ship  was  one  minute  east  of  the  observatory.  The  position  of 
the  ship  can  be  found  from  the  triangulation  of  the  bay  made  by  Mr.  Yery. 

With  regard  to  the  eclipse,  I  most  sincerely  regret  that  we  had  no  means  of  taking  photo- 
graphs. As  the  weather  happened  to  be,  this  was  the  one  thing  most  needful  for  us,  and  I  hope 
that  our  fortune  in  this  respect  may  be  a  warning  to  future  expeditions. 

DETEKMINATION  OF  TIME,  LATITUDE,  AND  LONGITUDE. 

§  1. 

The  observations  for  time  were  made  with  a  small  portable  transit  instrument  belonging  to  the 
United  States  Coast  Survey,  and  lent  for  the  occasion  by  Professor  Peirce,  the  Superintendent.  This 
instrument  has  an  axis  thirteen  inches  in  length  and  an  object-glass  of  1T7B  inch  aperture.  The 
magnifying  power  is  17.  On  first  setting  up  the  instrument  we  found  a  large  error  of  collimation, 
and  in  attempting  to  make  the  adjustment  the  head  of  one  of  the  adjusting  screws  twisted  off.  To 
supply  the  place  of  the  screw  a  spring  was  inserted  by  Mr.  Eogers  and  used  throughout  the  obser- 
vations. At  Mare  Island  the  transit  was  mounted  in  the  small  observatory  erected  for  Captain 
Brooke  in  1859.  The  stone  pier  having  been  displaced,  we  reset  it  and  bolted  a  two-inch  oak  plank 
carrying  the  supports  of  the  transit  to  this  pier.  The  observations  were  made  with  the  sidereal 
chronometer  Negus  1270,  and  by  the  eye  and  ear  method.  The  instrument  was  reversed  in  each 
series  of  observations.  The  level  was  read  as  often  as  once  in  twenty  minutes.  Before  beginning 
observations  the  errors  of  level  and  collimation  were  adjusted,  if  necessary,  and  then  no  further 
adjustments  made  during  the  night.  The  observations  have  been  reduced  in  the  following  manner. 
The  observed  time  of  transit  over  each  of  the  seven  wires  was  reduced  to  the  middle  wire  by  means 
of  the  equatorial  intervals,  and  the  corrections  for  level,  daily  aberration,  and  rate  of  chronometer 
were  applied  to  the  mean  of  the  seven  reduced  transits.  A  comparison  with  the  Ephemeris  gave  an 
approximate  value  of  the  correction  of  chronometer.  A  value  of  this  correction  was  then  assumed 
and  equations  of  condition  formed  in  the  usual  manner.  The  solution  of  these  equations  gave  the 
azimuth  and  collimation  errors  and  the  final  correction  of  the  chronometer.  The  following  are  the 
approximate  values  of  the  correction  of  the  chronometer  obtained  from  each  star : 


204 


EEPOET    OF   PROFESSOR    HALL. 
MARE  ISLAND. 


JUNE  17,  1869    ....         Observer,  Rogers. 

JUNE  19,  1869     ....         Observer,  Rogers. 

Star. 

Approx.  Corr. 

Wires. 

Circle. 

Star. 

Approx.  Corr. 

\Viiv*. 

Circle. 

h.  m.      s. 

ft.  m.      s. 

Polaris,  S.  P.     .     . 

—      3    4    0.87 

3 

W. 

Polaris,  S.  P.     .     . 

—      3    4    6.06 

2 

E. 

a    Virginis        .     .     . 

4  35.95 

7 

W. 

71    Bootis     .... 

4  40.81 

7 

E. 

)/    Ursa'  Majoris    .     . 

4  37.39 

5 

HE. 

a    Draconis      .     '. 

4  42.30 

5 

K. 

a    Draconis      ... 

4  40.85 

7 

E. 

a    Bootis  *  .... 

4  40.  46 

7 

E. 

a    Bootis     .... 

4  37.53 

7 

E. 

6    Bootis     .... 

4  40.39 

3 

E. 

0    Bootis     .... 

4  38.32 

6 

E. 

e     Bootis     .... 

4  40.08 

7 

E. 

e     Bootis     .... 

4  37.42 

7 

E. 

/?    Ursae  Miiioris   . 

4  41.73 

7 

E. 

a2   Librae     .... 

4  37.60 

6 

E. 

a2  Libra?     .... 

4  41.  15 

2 

E. 

/3    Ursoe  Minoris 

4  41.  49 

5 

E. 

(3    Libra?     .... 

4  38.71 

6 

W. 

/3    Librae     .... 

4  35.61 

7 

W. 

y2  Ursa)  Minoris    .     . 

4  39.33 

6 

W. 

y  Ursas  Minoris    . 

4  37.29 

7 

W. 

o    Serpeutis     .     .     . 

4  40.10 

7 

W. 

a    Coronas  Borealis    . 

4  36.35 

7 

W. 

a    Serpentis     .     .     . 

4  36.23 

7 

W. 

JUNE  18          .....         Observer,  Hall. 

JUNE  20-         Obscmr,  Hall. 

Polaris,  S.  P.     .     . 

—      34  29.04 

3 

E. 

Polaris,  S.  P.     .     . 

3    4  21.84 

2 

W. 

o    Virginis       ... 

4  39.53 

7 

E. 

a    Virgiuis       ... 

4  41.25 

7 

W. 

T]    Bootis     .... 

4  39.26 

7 

E. 

ri    Bootis     .... 

4  42.97 

7 

W. 

a    Draconis      .     .     . 

4  39.51 

7 

W. 

a    Draconis      .     .     . 

4  43.44 

2 

W. 

a    Bootis     .... 

4  39.22 

7 

W. 

a    Bootis     .... 

4  42.59 

7 

W. 

6    Bootis     .... 

4  40.69 

7 

W. 

e     Bootis     .... 

4  41.  12 

6 

E. 

e     Bootis     .... 

4  39.48 

7 

W. 

Clouds. 

a*  Librae     .... 

4  39.50 

7 

W. 

/I    Ursa?  Minoris   .     . 

4  38.74 

6 

W. 

/?    Librse     .... 

4  38.73 

7 

E. 

y3  Ursa;  Miuoris   . 

4  37.64 

7 

E. 

a    Coronas  Borealis    . 

4  38.52 

7 

E. 

a    Serpentis     .     .     . 

4  38.31 

7 

E. 

SEPTEMBER  28     ....         Observer,  Hall. 

SEPTEMBER  29        ...         Observer,  Rogers. 

<5    Draconis 

—      37  17.70 

7 

W. 

j8    Lyrao      .... 

—      3    7  19.58 

7 

W. 

S    Aquilse    .... 

7  18.41 

7 

W. 

f     Aquila?   .... 

7  18.38 

7 

W. 

K    Aquilae   .... 

7  18.48 

7 

W. 

6    Draconis 

7  16.37 

7 

W. 

y    Aquilse    .... 

7  18.22 

7 

W. 

S    Aquilae    .... 

7  19.14 

7 

W. 

a  'Aquilse   .... 

7  18.05 

7 

W. 

7    Aquilao   .... 

7  20.  47 

7 

E. 

(3    Aquilse   .... 

7  18.35 

7 

W. 

a    Aquilse   .... 

7  20.39 

7 

E. 

v    Capricorni  .     .     . 

7  17.29 

7 

E. 

f)    Aquila?   .... 

7  20.65 

7 

E. 

K    Cephei    .... 

7  11.45 

1 

E. 

K    Cephei    .... 

7  15.95 

7 

E. 

a    Cygni     .... 

7  15.35 

7 

E. 

e    Delphini      .     .     . 

7  20.  42 

7 

E. 

It    Aquarii  .... 

7  17.05 

6 

E. 

v    Cygni     .... 

7  15.94 

5 

E. 

At  Plover  Bay  the  transit  instrument  was  mounted  on  a  wooden  pier  filled  with  sand.  A  cover 
for  the  pier  was  made  of  pine  boards  fastened  together  with  wrought  nails,  and  the  o;ik  plank  was 
secured  to  this  cover  by  a  bolt.  The  weather  was  so  unfavorable  that  no  observations  could  be 


OBSERVATIONS    OF   THE    ECLIPSE    OF   AUGUST   7,    1869. 


205 


made  before  the  night  of  August  5,  when  the  sky  suddenly  became  partially  elear.  A  few  obser- 
vations were  made,  but  before  any  could  be  made  in  the  reversed  position  of  the  instrument  the  sky 
became  overcast.  On  examining  the  instrument  the  collimation  error  was  found  to  be  large,  and 
as  there  was  no  way  of  determining  it,  the  observations  of  the  5th  could  not  be  reduced.  On  the 
evening  of  the  Oth  the  instrument  was  brought  nearly  into  the  plane  of  the  meridian,  the  collima- 
tion and  level  errors  adjusted,  and  no  further  adjustments  attempted  during  the  night.  The  reduc- 
tions have  been  made  as  before,  save  that  here  an  approximate  value  of  the  azimuth  correction  was 
determined,  and  this  correction  has  been  applied  to  the  results  given  below. 

PLOVEli  BAY. 


AUGUST  6,  1869  Olwrm;  Rogers. 

Star. 

Approx.  Corr. 

Wires. 

Circle. 

h.   m.       s. 

y    Draconis  

—    6    30    14.82 

6 

W. 

30     14  62 

7 

W 

8     Lvr:i- 

30     14  80 

3 

W 

f     AquiliD     

30    13.96 

6 

W. 

30    14  76 

5 

W 

a     Cyr!ii 

30    14  24 

7 

W 

a     Cephei     

30    16.  10 

7 

W. 

30     13  99 

6 

E 

a    Aquarii 

30     15  02 

7 

E 

C     IVjjasi      

30    14.  93 

7 

E. 

a    IVgasi      

30    14.  44 

7 

E. 

These  observations  give  the  following  corrections  of  the  chronometer  Negus  1276 : 

Mare  Island,  June  17, 
18, 
19, 
20, 

Mare  Island,  Sept.  28, 
29, 

Plover  Bay,  Aug.    6, 

Sextant  observations  for  time  were  made  at  Plover  Bay  on  August  3d  and  4th.  These  observa- 
tions have  been  used  only  as  a  control,  and  I  have  preferred  to  depend  on  the  transit  observations 
for  time  and  longitude.  The  following  are  the  results.  The  pocket  chronometer  Dent  7986  was 
used  in  all  the  sextant  observations. 


Chron. 

time. 

h. 

m. 

S.                8. 

Observer. 

17>>. 

5 

—  3 

4 

37. 

29  ±0.15 

B. 

17". 

5 

—  3 

'  4 

39. 

14±0.15 

H. 

17h. 

5 

—  3 

4 

40. 

10±0.  17 

E. 

17U. 

5 

—  3 

4 

41. 

92  ±0.20 

H. 

23\ 

0 

—  3 

7 

16. 

98  ±0.05 

H. 

23h. 

0 

—  3 

7 

19. 

12  ±0.14 

B. 

3\ 

0 

—  6 

30 

14. 

59  ±0.17 

E. 

Date. 

Chron.  Time. 

Correction  of  Chron. 

Interpolated  Corr. 

No.  Alts. 

Observer. 

ft. 

h.    m.     s.              s. 

h.   m.      s. 

Aug.  3,     a.  m. 

2.63 

-    6    21    52.3    ±  1.37 

—      6    21    53.6 

12 

H. 

Aug.  4,    a.  m. 

2.65     . 

-    6    21    45.7    ±  0.52 

—      6    21     45.3 

15 

H. 

Aug.  4,    p.  m. 

8.92 

-    6    21    40.6    ±  1.29 

—      6    21    41.8 

15 

R. 

Aug.  4,    p.  m. 

9.70 

-    6    21    40.8    ±  0.56 

6    21    41.1 

16 

R. 

The  chronometer  Dent  7986  was  compared  with  the  sidereal  chronometer  immediately  before  and 
after  observing,  and"  column  4  gives  the  correction  deduced  from  these  comparisons,  the  correction 
of  the  sidereal  chronometer  having  been  found  by  means  of  its  daily  rate  from  the  transit  observa- 
tions of  August  6. 

If  we  observe  altitudes  near  the  prime  vertical,  the  difficulty  of  determining  the  time  will  increase 
very  nearly  as  the  cosine  of  the  latitude  diminishes,  and  in  high  latitudes  the  determination  becomes 


206 


REPORT  OF  PROFESSOR  HALL. 


uncertain.  Prom  all  the  observations,  58  altitudes,  I  find  the  probable  error  of  the  time  determined 
by  a  single  altitude  to  be  38.40.  As  an  example  of  our  work,  I  give  here  the  observation  of  August 
4,  a.  in. : 


Chronometer. 

Double  Alt. 

Corr.  Chron. 

Ti.   m.      «. 

O          I          II 

h.   m.      s. 

1    54    28.4 

48    58    30 

—  6    27    33.  3 

(1)  Index  Corr  =    +    38.7 

56    48.6 

49    27    30 

27    35.2 

57    29.5 

49    36    40 

27    32.3 

(2)  Index  Corr  +    33.  8 

Clouds. 

A  new  series. 

2    39      2.8 

59    10    50 

27    30.4 

Adopted    -f-    36  2 

39    50.4 

59    20      0 

27    31.  6 

o 

40    19.  0 

59    26      0 

27    30.2 

Thermometer     .     .     .     .     52.  5 

40    58.8 

58    30    40 

27    40.0 

Barometer                                29  61 

41    43.0 

58    40      0 

27    27.0 

A.  Thermometer     .     .     .     52.  2 

42    17.  6 

58    46    10 

27    30.  4 

43    32.0 

59      0    30 

27    32.8 

Reversed  horizon. 

44    23.2 

59    11     10 

27    29.0 

44    58.5 

59    17    50 

27    30.5 

46      0.5 

60    32    40 

27    32.9 

46    40.8 

60    41      0 

27    30.8 

47    20.8 

60    48    40 

27    31.5 

Mean  = 

—    6  27  31.  86 

§  2. 

The  observations  for  latitude  were  made  with  the  Pistor  &  Martins  patent  sextant,  No.  107. 
This  sextant  belongs  to  the  Naval  Academy,  and  was  procured  for  us  by  Professor  Coffin.  As  both 
of  the  observers  were  inexperienced  in  the  use  of  a  sextant,  and  being  desirous  to  know  the  quality 
of  the  work  done  by  such  an  instrument  in  su<5h  hands,  I  have  computed  the  latitude  from  each 
observed  altitude.  The  observations  were  made  in  sets  of  twelve  and  sixteen  altitudes,  taken  when 
the  sun  was  near  the  meridian.  They  were  made  symmetrical  with  respect  to  the  limbs  of  the  sun 
and  the  cover  of  the  horizon,  although  interruptions  by  clouds  sometimes  prevented  this  from  being 
done  completely. 

August  3.    Observer,  Rogers.  August  3.     Observer,  Rogers. 


23  47 

21  59 

22  23 
22  30 
22  23 
22  26 
22  30 
22  18 
22  20 
22  24 
22  25 
22  16 
22  28 
22  18 
22  24 
22  24 


=  +64  22  14 
22  17 
22  27 
22  20 
22  20 
22  23 
22  22 
22  17 
22  19 
22  28 
22  10 
22  35 
22  4 
22  47 
clouds 


64  22  22  ±1". 3 


64  22  22  ±1". 9 


OBSERVATIONS    OF    THE    ECLIPSE    OF   AUGUST   7,    1869.  207 

I  have  rejected  the  first  altitude  measured  in  which  there  appears  to  be  an  error  in  reading  the 
chronometer  or  sextant.    The  probable  error  of  the  latitude  from  a  single  altitude  is  6".l. 

August  4.    Observer,  Hall.  August  5.    Observer,  Hall.  August  5,  Observer,  Hall. 

o     i     if  o     /     n  o     i     ii 

<f  =  +61  22  40  <f=  +64  22  14  <p  =  +64  22  41 

22  30  22  35  22  29 

22    3  22  37  22  29 

22  27  22  27  22  33 

22  36  22    9  22  25 

22  38  22  32  22  11 

22  46  22  37  22  20. 

22  40  22  31  21  55 

22  26  22  20  22     5 

22  27  22  28  22    1 

22  39  22  38  22  24 

22  50  22  21  22  21 
22  18 
22  38 
22  20 
22  39 
22  32 


64  22  33  ±  1".9  64  22  27  ±  1".9  64  22  20  ±  2".7 

The  probable  error  of  the  latitude  from  a  single  altitude  is  7".8. 

Taking  the  mean  of  the  several  results  without  regard  to  the  probable  errors,  the  latitude  given 
by  the  sextant  is  <?  =  +  04°  22'  25". 

§  3. 

For  the  determination  of  longitude  ten  chronometers  were  used.  A  box  was  fastened  to  the 
floor  of  the  ship's  cabin,  and  in  this  the  case  for  the  chronometers  was  securely  fixed.  The  chro- 
nometers were  wound  and  compared  daily  at  about  9  o'clock  a.  m.,  and  the  temperature  of  the 
box  was  observed  generally  three  times  a  day,  at  9Ja.  m.,  2J  p.  m.,  and  at  9  p.  m.  The  temper- 
ature to  which  the  chronometers  were  exposed  was  quite  uniform,  and  until  September  21  the 
extremes  of  the  observed  temperatures  are  44°  and  64°.  After  our  return  and  while  lying  in  the 
harbor  of  San  Francisco,  the  temperature  rose  to  75°,  anil  this  increase  appeared  to  produce  small 
changes  in  the  rates  of  some  of  the  chronometers,  but  these  changes  are  so  small  and  occur  so  near 
the  end  of  the  voyage  that  they  will  not,  I  think,  seriously  affect  the  determination  of  longitude. 
The  ship's  9-inch  gun's  and  24-pound  howitzers  were  fired  a  few  times  on  July  C,  and  all  of  her 
guns  were  fired  repeatedly  September  20.  The  firing  of  July  6  produced  no  change  of  rate  that 
could  be  detected,  and  neither  did  that  of  September  20,  unless  the  small  changes  spoken  of  above 
and  ascribed  to  an  increase  of  temperature  were  produced  in  this  way. 

Two  excellent  chronometers  were  furnished  us  by  the  Messrs.  Negus,  of  New  York,  Nos.  1097 
and  1316,  of  their  own  make,  and  No.  1316  was  chosen  as  our  standard  chronometer  with  which  the 
others  were  compared.  At  Mare  Island,  through  the  kindness  of  Lieutenant  Commander  Merriman, 
we  procured  seven  additional  chronometers.  In  the  daily  comparison  the  chronometers  were  com- 
pared in  the  order  in  which  they  are  placed  below,  beginning  with  Negus  1276,  and  ending  with 
Negus  1298,  the  interval  between  the  comparison  of  two  chronometers  being  one  minute.  As  the 
sidereal  chronometer  Negus  1276  was  taken  out  of  the  ship  for  the  purpose  of  observing,  the  times 
of  comparison  are  not  so  uniform  with  it  as  with  the  others. 

The  chronometers  were—  Negus  1316    Negus  1097    Negus  599    Negus    1287    Negus  1317 

Negus  1276    Dent    2118    Negus  772    Desilva  694    Negus  1298 


208 


REPORT  OF  PROFESSOR  HALL. 


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s 

OBSERVATIONS    OP   THE    ECLIPSE    OF    AUGUST   7,    1869. 


209 


In  the  preceding-  table  the  first  column  of  dates  gives  the  times  of  the  comparisons  of  the  sidereal 
chronometer  Negus  1276,  the  second  column  the  times  of  the  comparisons  of  Negus  1298. 

I  have  now  assumed  a  constant  rate  for  each  chronometer,  and  with  these  rates  have  computed 
for  each  date  the  difference  between  the  standard  chronometer  and  each  of  the  chronometers. 
Subtracting  the  observed  difference  from  the  computed,  I  find  a  series  of  residuals,  the  mean  of 
which  for  each  date  is  assumed  to  be  the  correction  of  the  standard  chronometer.  Subtracting  the 
correction  of  the  standard  chronometer  from  the  first  residuals,  we  have  the  following  table : 


Negus 
1276. 

Negus 
1097. 

Dent 
2118. 

Negus 

599. 

Negus 
772. 

Negus 
1287. 

Desilva 
694. 

Negus 
1317. 

Negus 
1298. 

Negus 
1316. 

8. 

8. 

s. 

a. 

8. 

8. 

8. 

8. 

8. 

8. 

0.0 

0.0 

0.0 

0.0 

0.0 

0.0 

0.0 

0.0 

0.0 

0.0 

+     0.9 

+     3.3 

1.3 

+    4.1 

—    1.5 

+    0.8 

—    3.2 

—    2.8 

—    0.3 

—    0.2 

—    0.2 

+    5.2 

-    2.4 

+    8.2 

—    3.6 

—    0.3 

—    6.1 

+    0.7 

-    1.7 

—     1.3 

—     1.5 

+     5.7 

—    2.9 

+  10.2 

-    4.9 

—     1.0 

—    9.3 

+    5.3 

—    1.8 

1.5 

—    0.8 

+    7.1 

-    2.6 

+  11.9 

—    5.4 

—    0.8 

—    9.6 

+    2.1 

—    1.5 

—    0.8 

-     0.1 

+     9.0 

—    3.2 

+  12.2 

—    5.7 

—    0.2 

—    9.6 

—    0.8 

-    1.3 

-    0.4 

+     0.6 

+  10.3 

—    2.3 

+    8.3 

—    3.5 

+    0.8 

—    6.6 

-    6.6 

•    1.1 

+    0.9 

+     1.4 

+  10.0 

-    2.0 

+     5.4 

—    0.6 

—    0.6 

-    4.5 

-    9.7 

—    0.2 

+    2.3 

+    0.5 

+     9.7 

—    2.2 

+     4.9 

+    0.6 

+    0.1 

•    1.9 

—  10.8 

—     0.7 

+     2.0 

—    1.0 

+    8.9 

1.9 

+     0.1 

+     1.8 

—    0.3 

+    3.5 

-  11.5 

1.2 

+     2.4 

+     1.6 

+    6.9 

1.5 

1.7 

+     3.5 

—    0.5 

+    5.2 

-  11.0 

—    0.9 

+     1.2 

+     1.2 

+     5.9 

—    0.8 

—    3.7 

+     4.4 

1.6 

+    5.8 

—    9.0 

—    2.5 

+     1.2 

+     0.6 

+     5.5 

—     1.7 

—    6.6 

+     5.6 

•     1.3 

+    5.8 

—    5.3 

—    3.0 

+     1.3 

+     1.0 

+     4.3 

1.5 

-    9.4 

+     7.1 

+     0.1 

+    6.4 

-    6.4 

-    1.8 

+     2.4 

—     0.3 

+    .r>.  :i 

+     0.5 

—  11.7 

+    7.3 

+     1.6 

+    8.6 

-  11.0 

—    0.2 

+     3.2 

+     1.4 

+     5.3 

+     1.1 

-  10.9 

+     5.5 

+     1.3 

+    8.6 

-  12.6 

+    0.2 

+    2.5 

+     0.9 

+    5.1 

+     1.8 

-  10.2 

+    3.2 

+     1.3 

+    7.2 

—    9.2 

0.0 

+     1.6 

+     0.5 

+     4.0 

+     0.7 

—    5.4 

+     1.9 

+     1.0 

+    5.2 

-    7.5 

—    0.6 

+     0.4 

+     0.7 

+     3.6 

+     0.3 

-  10.4 

+    4.3 

+     0.7 

+     4.4 

—    3.5 

+    0.2 

+     1.7 

+     1.0 

+     1.7 

—    0.3 

-  10.4 

+    4.0 

+    0.4 

+     3.4 

—    0.5 

+    0.4 

+     1.9 

0.0 

0.0 

0.0 

0.0 

0.0 

0.0 

0.0 

0.0 

0.0 

0.0 

In  order  to  determine  the  relative  values  of  the  longitudes  given  by  the  chronometers,  it  is 
necessary  to  banish  from  these  residuals  all  law  of  sign.  Without  attempting  to  do  this  rigorously, 
or  to  introduce  a  coefficient  depending  directly  on  the  temperature,  it  is  sufficient  for  our  purpose 
to  assume  a  simple  function  of  the  time.  If,  therefore,  the  whole  interval  of  time  be  represented 
by  a  semi-circle,  I  find  the  following  expressions  for  the  rates: 


Negus  1316,  daily  rate 
Negus  1276,  daily  rate 
Negus  1097,  daily  rate 
Dent  2118,  daily  rate 
Negus  599,  daily  rate 
Negus  772,  daily  rate 
Negus  1287,  daily  rate 
Desilva  694,  daily  rate 
Negus  1317,  daily  rate 
Negus  1298,  daily  rate 

The  probable  errors  are  those  of  a  single 

27* 


=  —1.178—  1.4  sin  t  ±  0.8 
=  +1.554  ±  0.7 

=  _o.641—  7.2  sin  t  ±  1.4 
=  +7.337+  1.5  sin  t  ±1.0 
=  +3.492—11.6  sin  2  t  ±  1.8 
=  —0.691+  5.0  sin  2  t  =t  1.7 
=  +5.062  ±  0.6 

=  +1.746+  9.0  sin  2  t  ±  2.1 
=  +8.078+  9.0  sin  t  ±  3.0 
=  +2.297+  1.9  sin  t  ±  0.7 

interpolated  value. 


210 


REPORT  OF  PROFESSOR  HALL. 


From  the  observations  and  comparisons  at  Mitre  Island  we  have  the  following  corrections  of 
the  standard  chronometer  Negus  1316 : 

It.  m.      s.  Observer. 

June                   17.78C6  — 8  835.76            E. 

18. 7689  35. 22            H. 

19. 7735  33. 86            E. 

20. 7189  32. 96            H. 


Mean,  June 

September 


19.2620      8    8  3445 

28.6456  —  8     6  34.48 
29.6336  34.31 


H. 

E. 


Mean,  September          29.1396  —  8    634.40 


By  means  of  the  comparisons  of  the  chronometers  and  the  above  values  of  the  rates,  we  have 
the  following  corrections  on  local  time,  and  the  values  of  the  longitude  of  Plover  Bay  referred  to 
Mare  Island : 


Chronom- 
eter. 

Mare  Island, 
June  19.  2646. 

Reduction  for 
rate. 

Mare  Island, 
August  7.  9851. 

Plover  Bay, 
August  7.  98)1. 

Longitude. 

Ti.  m.  s. 

m.  s. 

Ik.  m.   s. 

h.  m.   s. 

It.  m.  s. 

1316 

8  8  34.  4 

+     1  0.0 

8  7  34.4 

•  11  31  55.7 

+   3  24  21.  3 

1276 

3  4  39.7 

1  17.3 

—   3  5  57.0 

—   6  30  16.  1 

24  19.1 

1097 

—   8  9  7.  6 

+     0  39.  1 

—   8  8  28.  5 

11  32  49.  8 

24  21.  3 

2118 

—  10  41  8.  0 

6  6.3 

-  10  47  14.  3 

14  11  35.3 

24  21.  0 

599 

—   8  46  18.  1 

2  53.6 

8  49  11.7 

•  12  13  34.4 

24  22.  7 

772 

—   7  46  18.7 

+     0  34.  4 

7  45  44.3 

•  11  10  6.5 

24  22.2 

1287 

—   9  26  2.  6 

4  11.7 

9  30  14.  3 

12  54  36.  8 

24  22.5 

694 

—   8  52  59.  9 

1  26.8 

8  54  17.  7 

12  18  42.  6 

24  15.9 

1317 

—  10  33  34.  6 

6  50.6 

-  10  40  25.  2 

14  4  48.2 

24  23.0 

1298 

8  10  34.2 

1  56.1 

—   8  12  30.  3 

•  11  36  51.  4 

24  21.  1 

Taking  the  mean  of  these  determinations  according  to  the  weights  indicated  by  the  probable 
errors,  and  considering  the  probable  errors  of  the  local  times,  we  have 

+  3h  24^  2i8.i  ±  (K36 

as  the  longitude  of  our  observatory  at  Plover  Bay  from  Mare  Island.  The  longitude  of  Mare 
Island  has  been  assumed  as  +8h  9m  18.0  from  Greenwich,  or  +3U  Om  49».0  from  Washington.  The 
longitudes  of  all  points  on  our  western  coast  are  referred  to  San  Francisco  as  a  standard  point,  and 
the  longitude  of  San  Francisco  has  been  deduced  from  the  observations  of  moon  culminations.  For 
the  present  I  take  as  the  longitude  of  Plover  Bay  from  Washington 

+6b  25m  10M 


The  following  observations  of  latitude  were  made  July  24  at  Illiouliouk,  on  the  Island  Una- 
laska.  The  observing  station  is  at  the  sun-dial  erected  by  the  Eussian  Fur  Company,  and  is  about 
eighty  yards  very  nearly  north  of  the  west  end  of  the  Greek  church.  The  longitude  has  been 
assumed  to  be  5h  57m  478.4  west  of  Washington. 

On  account  of  cloudy  weather,  no  observations  could  be  made  for  time,  and  those  for  latitude 
were  made  through  light  clouds.  Each  value  of  the  latitude  has  been  computed  from  the  mean  of 
five  observed  contacts. 


OBSERVATIONS    OF   THE    ECLIPSE    OF   AUGUST   7,    1869.  211 

HltouUouk. 

Q         I         II 

July  24,  I860,  <p=  +  53  52  60 

,52  58 
52  50 
52  39 
52  36 
52  27 
52  37 
52  39 
52  31 
52  26 
52  19 


y,  =  +  53  52  38±2".7 

At  Esquimalt,  Vancouver  Island,  sextant  observations  were  made  for  time  and  latitude,  and 
through  the  kind  permission  of  Captain  Edye,  li.  N.,  our  observing  station  was  on  Duntze 
Head,  the  point  to  which  the  longitudes  are  referred  in  the  elaborate  survey,  by  the  officers  of  the 
English  navy,  of  the  waters  around  Vancouver  Island.  The  following  are  the  results  obtained  for 
latitude,  each  value  depending  on  a  single  altitude : 

Duntze  Head. 


O   1   It 

O    '   " 

September  4,  1869,  y  =  +  48  25  47 

September  8,  1869,  <p  =  +  48  25  25 

37 

34 

40 

39 

39 

45 

33 

46 

58 

56 

31 

48 

52 

50 

37 

48 

58 

50 

65 

54 

63 

43 

35 

52 

9 

49 

62 

59 

49 

58 

67 

56 

48 

55 

<p=  +  48  25  45±2".o  <p  =  +  48  25  49±1".3 

Our  observations  for  time  give  the  following  corrections  of  the  standard  chronometer,  Negus 
1316,  on  local  mean  time ;  the  date  of  the  observations  being  expressed  in  the  time  of  this  chro- 
nometer : 

h    m        »         s 

1869,  Sept,  4.3417,  —  8  11  39.5±0.28by  16  altitudes  of  the  sun. 
1869,  Sept.  4.3417,  —  8  11  39.2±0.38  by  12  altitudes  of  a  Bootis. 

Adopted,  —  8  11  39.4  ±0.24 

A  set  of  twelve  altitudes  of  the  sun  observed  with  a  Dollond  sextant,  owned  by  Mr.  Very,  the 
navigator  of  the  United  States  Steamer  Mohican,  give  for  this  correction 

—  8h  llm  40S.6±08.35 


212 


REPORT  OF  PROFESSOR  HALL. 


The  comparisons  and  rates  of  the  chronometers  give  the  following  values  of  the  longitude  of 
Dnntze  Head  from  Mare  Island  Navy  Yard: 


Chronometer. 

Marti  Island, 
September  4.  3417. 

Duutze  i  oad, 
September  4.  3417. 

Longitude. 

Ncdis  1316 

Ti    m      s 

8724 

k    m          8 

8  11  39  4 

ll         III              8 

+     4  37  0±0  8 

Negus  1276 

—      3    6  39  5 

3  11  17  5 

_|_     4  38  o-^o  7 

Negus  1097 

8    8  12  1 

8  12  50  5 

-(-     4  38  4±1  4 

Dent  2118 

—     10  50  34  8 

10  55    97 

_j_     4  34  9^1  0 

—       8  50  57  8 

8  55  35  4 

-f-    4  37  6±1  8 

Negus  772 

—      7  45  21.2 

—      7  50    3  4 

-f-     4  42  2±1  7 

Ne^us  1287 

—      9  32  32.8 

—      9  37    9  4 

-f     4  36  6±0  6 

Desilva  694 

—      8  55    6.  3 

—      8  59  44  7 

_|_     4  38  4^2  1 

Negus  1317 

—     10  44    4.8 

—     10  48  45  2 

+     4  40  4±'i  0 

Negus  1298 

8  13  32.8 

—      8  18    9  2 

+     4  36  4±0  7 

Combining  the  several  results  according  to  their  weights,  the  longitude  of  Duntze  Head  from 
Mare  Island  is 

+  4m37B.l±08.40 

The  probable  errors  of  the  longitudes  given  by  the  single  chronometers  have  been  deduced  by 
comparing  the  rates  of  the  chronometers  among  themselves,  and  serve  only  for  a  combination  of 
the  various  results. 

The  real  probable  error  of  the  final  result  is  no  doubt  greater  than  that  given  above  ;  but  to 
determine  it  would  require  an  investigation  of  the  temperature  coefficients,  and  the  stationary  and 
traveling  rates  of  each  chronometer.  Assuming  the  longitude  of  our  observing  station  on  Mare 
Island  to  be  8h  9m  18.0  west  of  Greenwich,  the  longitude  of  Duutze  Head  is,  by  our  observations, 

8h   13™  38s.l 
The  position  of  Duntze  Head  given  in  the  English  survey  is 

Latitude  =  +  48°  25'  49" 
Longitude  =  +  8U  13m  478.1 

An  increase  of  the  longitude  of  Mare  Island  will  probably  result  from  the  telegraphic  determi- 
nation of  the  longitude  of  San  Francisco  by  the  United  States  Coast  Survey ;  and  this  will  bring 
the  preceding  results  for  longitude  into  better  agreement. 

The  sextant  observations  were  made  by  Mr.  Joseph  A.  Eogers  and  myself,  both  of  us  generally 
taking  part  in  the  observation,  one  using  the  sextant  and  the  other  observing  the  time. 

As  our  determinations  of  latitude  depend  on  the  Pistor  &  Martin's  Patent  Sextant  No.  107, 1 
have  made  a  series  of  measurements  of  the  distances  between  known  stars  in  order  to  test  the 
work  of  this  sextant. 

The  following  table  gives  the  results  of  these  measurements : 


Objects. 

Distance. 

Errors. 

No.  of  measure- 
ments. 

a  Arietis  to  /?  Arietis  

o 
3.9 

//        // 
+    9.  1±3.6 

20 

a  Tanri  to  fi  Tanri  

16.8 

+    2.  4±3.  1, 

14 

34  2 

—    7.  3±4.  3 

20 

66  8 

—    7.2±3.7 

19 

a  Tauri  to  a  UrsiE  Minoris  

72.8 
93  3 

+    1.0±2.7 
—  10.0±3.0 

12 
15 

115  2 

—    1.  1±5.7 

15 

OBSERVATIONS    OF    THE    ECLIPSE    OF   AUGUST    7,    1869. 


213 


The  resulting  errors  are  so  small  and  of  such  a  character  that  I  shall  not  make  any  correction 
of  the  sextant  observations.  Prom  the  115  measurements,  the  average  probable  error  of  a  single 
measured  distance  is  15".  1. 

All  the  astronomical  observations  were  recorded  on  loose  sheets  of  paper,  and  soon  after,  gen- 
erally the  next  day,  they  were  copied  into  blank-books.  The  observations  are  deposited  at  the 
Xaval  Observatory  and  can  be  referred  to  at  any  time  if  need  be. 

MAGNETIC   OBSERVATIONS. 

§  I- 

The  observations  for  magnetic  declination  at  Plover  Bay  were  made  with  a  compass  needle  6£ 
inches  in  length.  The  compass  circle  is  divided  to  30'.  A  sharp,  pointed  rock  off  West  Head,  and 
very  near  the  sea  horizon,  was  selected  as  the  point  of  reference  in  azimuth.  The  azimuth  of  this 
rock  was  determined  by  sextant  observations,  on  August  4th  and  Oth.  The  azimuths  deduced  from 
the  observations  are  <>1>0  0'.3  and  01°  58'.5,  counting  from  the  south  towards  the  west,  and  the  mean 
value  01°  5!V.4  has  been  adopted.  The  declination  was  determined  also  by  direct  observations  of 
the  sun  on  August  3,  4,  and  5.  The  observation  of  August  4  was  made  through  clouds, 
but  as  it  has  the  advantage  of  a  different  position  of  the  sun,  it  has  received  the  same  weight  as 
the  others.  The  following  are  the  results  obtained. 


D;itc. 

Object  observed. 

Declination. 

Observer. 

1869.          7i.     m. 

o         / 

Aug.  3.         6     55     j>.  in. 

Sun. 

19    42.  2    East. 

H. 

4.         fl    l!4     a.m. 

Sun. 

19    54.  3 

H. 

5.         4     30     p.  in. 

Pinnacle. 

19    30.0 

H. 

5.         50     p.  HI. 

Pinnacle. 

19    34.6 

H. 

5.         6      7     p.m. 

Sun. 

19    39.0 

H. 

o        / 

Mean  value 

19    40.  0    East. 

The  observations  for  dip  and  intensity  were  made  with  the  Barrow  dip  circle  No.  4,  lent  to  us 
by  Professor  Peirce,  Superintendent  of  the  Coast  Survey.  The  vertical  circle  of  this  instrument 
has  a  diameter  of  Di  inches,  and  is  divided  to  10'.  The  instrument  is  furnished  with  two  common 
needles  for  observing  the  dip,  and  with  two  Lloyd  needles  for  observing  the  relative  intensity.  In 
observing,  it  was  mounted  on  a  tripod,  and  the  observations  were  made  in  open  air,  without  pro* 
tection  for  the  instrument.  The  instrument  was  first  leveled,  then  the  plane  of  the  vertical  circle 
was  made  perpendicular  to  the  magnetic  meridian  by  using  one  of  the  needles,  and  finally  brought 
into  that  meridian  by  means  of  the  horizontal  circle.  The  readings  and  reversals  were  then  made 
in  the  usual  manner.  During  an  observation  with  a  Lloyd  needle,  the  thermometer,  Fahrenheit, 
was  read  four  times,  and  the  thermometer  was  placed  so  as  to  give  the  temperature  of  the  needle 
as  nearly  as  the  observer  could  judge.  The  Lloyd  needle  was  used  first  without  the  weight,  then 
with  the  weight  in  the  inner  hole,  then  with  the  weight  in  the  outer  hole,  and  lastly,  without  the 
weight.  The  mean  of  the  first  and  last  observations  was  taken  as  the  dip  of  the  unloaded  needle. 
The  weights  were  inserted  in  the  A  ends  of  the  needles,  a  weight  having  been  provided  for  each 
needle.  The  observations  were  recorded  in  convenient  forms  furnished  by  Professor  Harkness. 

In  the  following  table  of  results  0  and  o1  denote  the  dip  of  the  needle  with  the  weight  in  the 
inner  and  outer  holes: 


214 


REPORT    OF   PROFESSOR    HALL. 
OBSERVATIONS  OF  MAGNETIC  1)11'. 


Date. 

Station. 

Needle  1. 

Net-die  2. 

Temp. 

Observer. 

1869.            h.  m. 

o         / 

0              / 

o 

May    15.         9  10  a.  m. 

Washington. 

71     15.  0 

71    23.4 

69.0 

H. 

Dec.      1.         1  38  p.m. 

Washington. 

71      6.1 

71    34.6 

57.0 

H. 

2.         0    0  m. 

Washington. 

71      6.5 

71    52.  7 

56.0 

H. 

Aug.     4.         9  30  a.  in. 

Plover  Bay. 

74    41.3 

74    35.5 

54.0 

H. 

4.         10  p.  m. 

Plover  Bay. 

74    36.6 

74    34.7 

55.0 

R. 

5.       10    0  a.m. 

Plover  Bay. 

74    41.3 

74     43.  4 

49.0 

H. 

Sept.    6.       11    0  a.m. 

Esquimalt  Navy  Yard. 

70    46.  3 

71     20.  0 

72.0 

H. 

7.         0  12   p.m. 

Esquimalt  Church. 

70    59.  8 

70     55.  6 

67.6 

R. 

9.       11    7   a.m. 

Esquimalt  Church. 

71     17.  8 

71     27.0 

80.8 

H. 

23.         14  p.m. 

Yerba  Buena. 

60    32.5 

63      6.8 

92.9 

R. 

24.         9  55  a,  m. 

Yerba  Buena. 

62      5.6 

64     14.  7 

81.5 

H. 

OBSERVATIONS  WITH  THE  LLOYD  NEEDLES. 


Date. 

Time. 

Station. 

Needle. 

Dip. 

9. 

ei. 

Temp. 

Obs'r. 

1869. 

h.  m. 

o      / 

c        / 

0           1 

o 

May    15 

10  15a.m. 

Washington       ... 

1. 

71  48.5 

—23  42.  4 

—50  23.  8 

74.0 

H. 

10  45  a.  m. 

Washington       ... 

2. 

70  55.6 

—37  23.2 

—56  23.  0 

76.0 

H. 

Dec.      1 

2  10p.m. 

Washington        ... 

1. 

72  29.  2 

—20  19.8 

—42  51.  9 

50.2 

H. 

2  50  p.  m. 

Washington        ... 

2. 

71  25.4 

—35  40.  8 

—55    9.2 

47.2 

H. 

2 

0  32  p.  m. 

Washington       ... 

1. 

72  26.  8 

—14    6.7 

—39  20.  5 

55.0 

H. 

0  54  p.  m. 

Washington       ... 

2. 

71  25.6 

—34  59.5 

—54  58.5 

49.6 

H. 

June  23 

10  45a.m. 

Yerba  Buena      ... 

1. 

63    5.8 

—35  35.  7 

—54  20.  2 

70.1 

H. 

11  50a.m. 

Yerba  Buena 

2. 

63  39.  0 

—47    7.8 

—58  39.  0 

76.7 

H. 

24 

11  23  a.  m. 

Yerba  Bnena      -     -     - 

1. 

62  27.9 

—36  14.5 

—50  13.2 

63.9 

R. 

0    7p.m. 

Yerba  Buena      .     .     . 

2. 

61  12.4 

—45  59.  0 

—56  59.0 

66.2 

R. 

Sept.  23 

0  41  p.m. 

Yerba  Buena      .     .     . 

1. 

63  49.  1 

—39  33.5 

—49  49.  0 

92.5 

R. 

0  16p.m. 

Yerba  Buena      .     .     . 

2. 

62    3.0 

—44  42.  5 

—56  40.5 

92.9 

R. 

24 

10  23  a.  m. 

Yerba  Buena      ... 

1. 

63  44.  8 

—33  30.7 

—49    4.2 

80.0 

H. 

10  45a.m. 

Yerba  Buena      ... 

2. 

62  15.0 

—44    3.8 

—56  51.  2 

80.9 

H. 

Aug.      3 

6    0  p.  m. 

Plover  Bay    .... 

1. 

74  54.3 

—37  45.  8 

—60  19.5 

50.2 

H. 

6  30  p.  m. 

Plover  Bay    .... 

2. 

75  16.2 

—51     1.0 

—64  48.5 

48.4 

H. 

4 

11  30a.m. 

Plover  Bay    .... 

1. 

76  16.4 

—37  21.5 

—57  34.0 

59.5 

R. 

0  15p.m. 

Plover  Bay    .... 

2. 

74  30.2 

—52  27.  8 

—67     1.0 

63.1 

R. 

5 

11     0  a.  m. 

Plover  Bay    .... 

1. 

75  35.  1 

—29  33.0 

—60  34.  8 

51.8 

H. 

1    0  p.  m. 

Plover  Bay    .... 

2. 

74  46.5 

—51  54.5 

—65  50.0 

50.0 

H. 

Sept.     4 

1  23p.m. 

Esquimalt  Navy  Yard 

1. 

72  59.  3 

—28  42.  0 

—49  19.0 

64.3 

H. 

2    4p.m. 

Esquimalt  Navy  Yard 

2. 

71  30.0 

—42  15.2 

—56  42.  8 

67.0 

H. 

6 

0    Om. 

Esquimalt  Navy  Yard 

1. 

72  10.2 

—30  56.  5 

—45  45.  8 

76.0 

H. 

0  40p.m. 

Esquimalt  Navy  Yard 

2. 

71  45.4 

—41  55.0 

—57  23.8 

74.5 

H. 

Sept.     7 

11  10a.m. 

Esquimalt  Church  .     . 

1. 

73    1.6 

—29  50.  5 

—44  44.0 

64.6 

R. 

11  40a.m. 

Esquimalt  Church  . 

2. 

71  25.  0 

—41  26.7 

—58    7.5 

67.0 

R. 

9 

11  30a.m. 

Esquimalt  Church  . 

1. 

73    9.3 

—27  55.2 

—50  11.0 

75.5 

H. 

0    Om. 

Esquimalt  Church  . 

2. 

71  28.1 

—41  31.2 

—58  11.5 

70.2 

H. 

OBSERVATIONS    OF   THE    ECLIPSE    OF    AUGUST   7,    1869. 


215 


The  temperature  at  Yerba  Bueiia  was  observed  in  June  with  one  of  the  ship's  thermometers. 
This  thermometer  had  a  graduation  on  the  tube,  and  also  a  graduated  scale  attached.  The  two 
graduations  differed  as  much  15°  in  the  higher  temperatures.  The  graduation  on  the  tube  was 
used  in  the  observations;  but  a  few  days  after,  and  before  any  comparison  with  our  own  thermome- 
ters, this  thermometer  was  broken. 

In  September  the  station  at  Yerba  Buena  was  intensely  hot. 

The  magnetic  station  at  Washington  is  in  Mr.  Schott's  garden  on  Capitol  Hill;  at  Yerba 
Buena,  the  station  is  on  the  beach  at  high-water  mark,  and  150  feet  north  of  the  government  pier 
on  the  eastern  side  of  the  island — the  same  that  was  occupied  by  Professor  Harkness  in  1866;  at 
Plover  Bay,  near  our  observatory  on  the  sand  pit ;  at  Esquimault  navy  yard,  about  40  feet  west 
of  the  entrance  gate  in  the  open  yard  north  of  the  road  ;  and  at  Esquiiuault  church.  50  feet  west  of 
the  English  church,  near  the  signal  staff  erected  by  the  United  States  Coast  Survey.  The  geograph- 
ical positions  of  these  places  are  as  follows,  the  longitudes  being  reckoned  from  Greenwich: 


Place. 

Latitude. 

Longitude. 

Washington       
Yerba  Buena      

o        / 
38  53.  1  north 
37  48.8      " 
64  22.4       " 

o        / 
76  59.  9  west 
122  20.  7      " 
173  19.5       " 

Egquimalt  Navy  Yard 
Esquimau  Church       .     .     . 

48  25.  8      " 
48  25.  0      " 

123  26.  5      " 
123  26.  0      " 

For  the  value  of  the  magnetic  dip  to  be  used  in  computing  the  relative  values  of  the  magnetic 
force,  I  have  taken  for  each  station  the  means  of  the  values  observed  with  the  common  needles. 
The  values  of  the  dip  given  by  these  needles  are  as  follows  : 


Washington - 71  19.2 

Washington 71  24.  7 

Plover  Bay,  Siberia 74  38. 8 

Esquimalt,  Vancouver  Island 71     7.  7 

Yerba  Buena  .  62  29.9 


(May.) 
(December.) 


By  comparing  the  above  values  of  the  dip  with  the  values  given  by  the  Lloyd  needles,  the  cor- 
rections for  these  needles  are, 

Needle  1,  s  =  —  65'.6  ;  Needle  2,  c  =  —  4'.5 

The  observations  at  Washington  give  the  only  means  of  estimating  the  effect  of  a  change  of 
temperature  on  the  values  of  the  dip  given  by  the  Lloyd  needles.  .  Hence  we  have 

Needle  1,  A5=—  I'M  At-,  Needle  2,  A3  =  —  I'M  At. 

The  values  of  the  coefficients  have  been  found  from  a  change  of  temperature  of  25°  ;  but  an 
examination  of  the  observations  will  show  that  disturbance  from  other  sources,  probably  a  slight 
rusting  of  the  needles,  is  so  great  that  it  is  not  worth  while  to  apply  any  correction  for  temperature. 

If  if  be  the  total  magnetic  force  at  a  station,  S  the  corrected  dip  of  the  Lloyd  needle,  and  0  the 
dip  of  the  needle  when  loaded  with  a  weight,  and  <p^  3^  ol  denoting  similar  quantities  at  another 
station,  we  shall  have  by  Dr.  Lloyd's  method  — 


<f  _cos  0  .  sin  (<*i  —  0i) 
¥>i~cos  0j.  sin  (S  —  e)' 


216 


REPORT  OF  PROFESSOR  HALL. 


Our  observations  give  the  following  values  of  S  and  0;  two  values  of  <>  being  observed  with 
each  needle  as  the  weight  was  inserted  iu  the  hole  nearest  and  farthest  from  the  axis : 


Station. 

Needle. 

<i 

H 

«' 

Washington  .  . 

1 

O            1 

71    2  6 

o         / 
20  27  3 

0           ' 

36  21  6 

Washington  . 

2 

71     6  0 

45  45  0 

55  43  4 

Yei'lja  Buena.  

1 

62    9  3 

36  13  6 

45  28  3 

Yerba  Bueiia.  .  . 

2 

62  12  9 

50  51  7 

57  17  4 

Plover  Bay    .... 

1 

74  29  7 

34  53  4 

51  47  8 

Plover  Bay  

2 

74  46  5 

59  29  4 

65  53  2 

Ksquiiualt  

1 

71  44  5 

29  21  0 

41  47  1 

Esquinialt  

2 

71  27  6 

47  30  0 

57  36  4 

Assuming  that  the  force  at  Washington  is  expressed  by  the  number  13.35,  (in  English  units,) 
the  forces  at  the  stations  are  found  to  be  as  follows : 

Yerba  Buena,  force  =  11.  61 
11.64 
11.  71 
11.78 


Mean  =  11. 68 

Plover  Bay,  force  =  12. 38 
11. 90 
11.96 
12.23 


Mean  =  12. 12 

Esquinialt,  force  =  12.  65 
12.83 
13.22 
13.09 


Mean  =  12.  95 

After  our  return  to  Washington  an  examination  of  the  needles  shows  that  they  have  rusted  a 
little,  a  condition  not  surprising  considering  the  long  sea  voyage. 

I  am  very  much  indebted  to  Mr.  C.  A.  Schott,  of  the  United  States  Coast  Survey,  for  instruc- 
tion and  advice  in  using  the  magnetic  instruments. 

BAEOMETER  AND  THEEMOMETEE. 

The  barometer  used  at  Plover  Bay  is  a  mercurial  ship  barometer,  made  by  Green,  of  New  York. 
We  had  no  opportunity  of  comparing  it  with  a  standard  barometer.  The  thermometers  are  No. 
38  and  No.  39,  by  Negretti  and  Zambra,  of  London.  They  were  exposed  so  as  to  give  the  temper- 
ature of  the  air  in  the  shade.  By  comparison  with  the  standard  thermometer  of  the  Naval  Obser- 
vatory Professor  Eastman  found  that  these  thermometers  require  the  correction  respectively  of 
+0°.2  and  +0°.3,  and  a  comparison  since  our  return  shows  that  these  corrections  have  not 
changed.  No  corrections  have  been  applied  to  the  observations  following: 


OBSERVATIONS    OF    THE    ECLIPSE    OP    AUGUST   7,    1860. 


217 


Date. 

Hour. 

Barometer. 

At.  Ther. 

Ther.  No.  38. 

Ther.  No.  39. 

li.     m. 

in. 

O 

o 

o 

1869.  Aug.  1 

7       0     p.  m. 

29.  74 

50.0 

50.2 

50.0 

2 

10      0    a.  in. 

29.78 

48.0 

47.3 

47.1 

2 

8    15    p.  m. 

29.79 

48.7 

48.3 

48.5 

3 

8    15    a.  in. 

29.90 

52.2 

54-.0 

53.8 

3 

3      0    p.  m. 

29.90 

54.5 

53.2 

53.0 

3 

6    45     p.  in. 

29.86 

50.8 

47.3 

47.2 

4 

7     15    a.m. 

29.  61 

52.2 

52.7 

52.4 

4 

1     15     p.  m. 

29.58 

57.2 

55.4 

55.3 

4 

3     45     p.  in. 

29.  58               56.  0 

56.6 

56.4 

4 

7     45     p.  in. 

29.61 

51.6 

51.6 

51.4 

5 

8       (1     a.m. 

29.  55              46.  6 

46.0 

45.  H 

5 

12       0     in. 

29.  62               51.  7 

49.9 

49.7   ' 

5 

6    30     p.  m. 

29.  72               55.  3 

47.5 

47.2 

6 

8     45     a.m. 

29.  56               46.  5 

45.  2 

45.0 

6 

3     45    p.  in. 

29.  49               56.  5 

55.2 

55.  4 

6 

11       0     p.  m. 

29.  65               46.  3 

44.4 

44.4 

7 

7       0     a.m. 

29.  83 

7 

11     15     a.  m. 

29.  90              49.  4 

55.0 

55.1 

When  about  leaving  Washington  I  received  from  Mr.  W.  H.  Ball  a  Smithsonian  blank  for  a 
comparative  vocabulary  of  the  natives  at  Plover  Bay.  This  blank  I  filled  up,  and  in  doing  this  I 
was  assisted  by  Mr.  William  E.  White,  who  has  been  engaged  for  several  years  in  trading  on  that 
coast.  From  Lieutenant  Commander  Louis  Kernpff,  United  States  Navy,  I  have  a  pretty  full 
vocabulary  of  the  Indians  of  our  northwestern  coast  and  of  Vancouver  Island. 

I  am  very  much  obliged  to  Professor  Coffin,  Superintendent  of  the  Nautical  Almanac,  through 
whose  kindness  we  were  provided  with  several  instruments,  and  at  whose  request  Professor  B.  Otis 
Kendall  procured  from  the  University  of  Pennsylvania  the  telescope  used  by  Mr.  Rogers  in  observ- 
ing the  eclipse.  I  am  also  under  obligations  to  Mr.  John  Downes,  of  the  Nautical  Almanac,  who 
computed  the  occultations  of  several  stars  visible  at  Plover  Bay. 

Finally,  1  tender  my  sincere  thanks  to  Mr.  Joseph  A.  Eogers,  of  the  United  States  Hydro- 
graphic  Office,  my  companion  in  the  expedition,  who  did  everything  possible  to  make  our  success 
complete. 

Very  respectfully,  your  obedient  servant, 

ASAPH  HALL, 

Professor  of  Mathematics  U.  8.  Navy. 
Connnodore  B.  F.  SANDS,  U.  S.  N., 

Superintendent  of  the  U.  S.  Naval  Observatory,  Washington,  D.  C. 

28* 


© 


X 
4- 


o 


t- 


o 

x 

^ 
W 

— : 
-ce 


CD 
*-J 

cti 

i — I 

PH 


"C5 


a 
o 


ce 

0) 


gg 

IV 

Q 


ri 

O 
0< 

W 


& 


Plate  HI. 


•miANGVLATION 

CONNECTINGTHE 

TEMPORARY  OBSERVATORIES 

AT 

DES  MOINKS,IOWA, 

IN 

AUGUST      1869. 


Srale, 


Naval     <s,-' 
Observatory  \^x 
West  Signal 


North  Base 


East  Signal 


latohfield 
O  \i  s  ervHtory 


O  iOO  2OO  tlOO  -*OO  .TOO  ftOO  7OO    Metres 


2000  ajoo  Feet . 


IVoCWm  Harkness.U.S.N.del. 


J.Bien  I. Hi 


Plate  IV 


THE   SPECTROSCOPE 


.l.Bien  lith 


Plate  V. 


Sun 


n 


in. 


IV 


V. 


Seal  (•    of     Tin  Is  . 


./'  .7 


Spectra    observed. 


Pn.lMV  Hnrklii-KS  I'  >  \.,1,-1 


KMorns  clirinnohrti 


II  ll 


N'oon 


-Mi. 


PLATKim. 

6JL. 


r/er/ifm/ /rn 


I'llVW 


n/j.vtr\rffiijft.v>i-iffi  the  Photometer. 


f 


f'ntw 


ran  ob»er\-atianjsiv't}>  the  Actinontelt  f  Avff. 


IO.O 


0.0 


lix'ttKiinv  ti/'  ('(ii'iiiin   mill   /Jittfutiririnr<'.v  irntnrtlititfty  ajlrr 


of  CffT"ontt-   etfj^ef   Pt'otuliemn  fe..v  /rtst    £r/*W 
of  7'otafity. 


rnrt 


Plate  X. 


1)1.  K. Ciii-lia.  L'.S.A  .ph'it". 


TOTAL     ECLIPSE    OF    THE   SUN,  AUGUST  77?   1869. 

Appearance   of  Phenomena   after  comiiiciiceinem  of  Totality. 

Fac- simile  of  Photograph   N°  62. 


Plate  XI . 


Dr.E. Curtis  t'.S. A  .photo. 


.I.Bien    lith. 


TOTAL     ECLIPSE   OF    THE   SUN,  AUGUST  7™  1869. 

Appearance  of  Phenomena   near  the  close  of  Totality 

Fac- simile  of  Photograph  N°  63. 


The  Coiona  of  the  Total  Eclipse  uf  August  7.1869,  as  seenhythe  aid 
of  a  four  inch  tele  sc  OL  P 


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